diff --git a/spring-boot/configuration/.gitignore b/spring-boot/configuration/.gitignore
new file mode 100644
index 0000000..d6819a4
--- /dev/null
+++ b/spring-boot/configuration/.gitignore
@@ -0,0 +1,26 @@
+.gradle
+/build/
+!gradle/wrapper/gradle-wrapper.jar
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+/out/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
diff --git a/spring-boot/configuration/build.gradle b/spring-boot/configuration/build.gradle
new file mode 100644
index 0000000..5ada682
--- /dev/null
+++ b/spring-boot/configuration/build.gradle
@@ -0,0 +1,31 @@
+plugins {
+	id 'org.springframework.boot' version '2.1.3.RELEASE'
+	id 'java'
+}
+
+apply plugin: 'io.spring.dependency-management'
+
+group = 'io.reflectoring'
+version = '0.0.1-SNAPSHOT'
+sourceCompatibility = '11'
+
+repositories {
+	mavenCentral()
+}
+
+dependencies {
+	implementation 'org.springframework.boot:spring-boot-starter'
+	implementation 'org.springframework.boot:spring-boot-starter-mail'
+	implementation 'org.springframework.boot:spring-boot-starter-validation'
+	compileOnly 'org.projectlombok:lombok'
+	annotationProcessor 'org.projectlombok:lombok'
+	annotationProcessor 'org.springframework.boot:spring-boot-configuration-processor'
+	testImplementation('org.junit.jupiter:junit-jupiter:5.4.0')
+	testImplementation('org.springframework.boot:spring-boot-starter-test'){
+		exclude group: 'org.junit', module: 'junit'
+	}
+}
+
+test {
+	useJUnitPlatform()
+}
diff --git a/spring-boot/configuration/gradlew b/spring-boot/configuration/gradlew
new file mode 100644
index 0000000..af6708f
--- /dev/null
+++ b/spring-boot/configuration/gradlew
@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"
diff --git a/spring-boot/configuration/gradlew.bat b/spring-boot/configuration/gradlew.bat
new file mode 100644
index 0000000..6d57edc
--- /dev/null
+++ b/spring-boot/configuration/gradlew.bat
@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/spring-boot/configuration/settings.gradle b/spring-boot/configuration/settings.gradle
new file mode 100644
index 0000000..df58ca7
--- /dev/null
+++ b/spring-boot/configuration/settings.gradle
@@ -0,0 +1,6 @@
+pluginManagement {
+	repositories {
+		gradlePluginPortal()
+	}
+}
+rootProject.name = 'configuration'
diff --git a/spring-boot/configuration/src/main/java/io/reflectoring/configuration/ConfigurationApplication.java b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/ConfigurationApplication.java
new file mode 100644
index 0000000..895c720
--- /dev/null
+++ b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/ConfigurationApplication.java
@@ -0,0 +1,13 @@
+package io.reflectoring.configuration;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class ConfigurationApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(ConfigurationApplication.class, args);
+	}
+
+}
diff --git a/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/MailModuleConfiguration.java b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/MailModuleConfiguration.java
new file mode 100644
index 0000000..2918bbc
--- /dev/null
+++ b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/MailModuleConfiguration.java
@@ -0,0 +1,18 @@
+package io.reflectoring.configuration.mail;
+
+import org.springframework.boot.context.properties.ConfigurationPropertiesBinding;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+@EnableConfigurationProperties(MailModuleProperties.class)
+class MailModuleConfiguration {
+
+	@Bean
+	@ConfigurationPropertiesBinding
+	public WeightConverter weightConverter() {
+		return new WeightConverter();
+	}
+
+}
diff --git a/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/MailModuleProperties.java b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/MailModuleProperties.java
new file mode 100644
index 0000000..ce78c31
--- /dev/null
+++ b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/MailModuleProperties.java
@@ -0,0 +1,84 @@
+package io.reflectoring.configuration.mail;
+
+import javax.validation.constraints.NotEmpty;
+import javax.validation.constraints.NotNull;
+
+import java.time.Duration;
+import java.util.List;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.boot.context.properties.DeprecatedConfigurationProperty;
+import org.springframework.util.unit.DataSize;
+import org.springframework.validation.annotation.Validated;
+
+@ConfigurationProperties(prefix = "myapp.mail", ignoreInvalidFields = true, ignoreUnknownFields = false)
+@Validated
+class MailModuleProperties {
+
+  @NotNull
+  private Boolean enabled = Boolean.TRUE;
+
+  @NotEmpty
+  private String defaultSubject;
+
+  @NotNull
+  private Duration pauseBetweenMails;
+
+  @NotNull
+  private DataSize maxAttachmentSize;
+
+  @NotNull
+  private Weight maxAttachmentWeight;
+
+  @NotEmpty
+  private List<String> smtpServers;
+
+  @DeprecatedConfigurationProperty(reason = "not needed anymore", replacement = "none")
+  public String getDefaultSubject() {
+    return defaultSubject;
+  }
+
+  public Boolean getEnabled() {
+    return enabled;
+  }
+
+  public void setEnabled(Boolean enabled) {
+    this.enabled = enabled;
+  }
+
+  public void setDefaultSubject(String defaultSubject) {
+    this.defaultSubject = defaultSubject;
+  }
+
+  public Duration getPauseBetweenMails() {
+    return pauseBetweenMails;
+  }
+
+  public void setPauseBetweenMails(Duration pauseBetweenMails) {
+    this.pauseBetweenMails = pauseBetweenMails;
+  }
+
+  public DataSize getMaxAttachmentSize() {
+    return maxAttachmentSize;
+  }
+
+  public void setMaxAttachmentSize(DataSize maxAttachmentSize) {
+    this.maxAttachmentSize = maxAttachmentSize;
+  }
+
+  public List<String> getSmtpServers() {
+    return smtpServers;
+  }
+
+  public void setSmtpServers(List<String> smtpServers) {
+    this.smtpServers = smtpServers;
+  }
+
+  public Weight getMaxAttachmentWeight() {
+    return maxAttachmentWeight;
+  }
+
+  public void setMaxAttachmentWeight(Weight maxAttachmentWeight) {
+    this.maxAttachmentWeight = maxAttachmentWeight;
+  }
+}
diff --git a/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/Weight.java b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/Weight.java
new file mode 100644
index 0000000..21dc2e5
--- /dev/null
+++ b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/Weight.java
@@ -0,0 +1,39 @@
+package io.reflectoring.configuration.mail;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class Weight {
+
+	private static final Pattern PATTERN = Pattern.compile("^([0-9]+)(g|kg|t)$");
+
+	private long grams;
+
+	private Weight(long grams){
+		this.grams = grams;
+	}
+
+	public static Weight fromString(String string) {
+		Matcher matcher = PATTERN.matcher(string);
+		if (matcher.matches()) {
+			Long amount = Long.valueOf(matcher.group(1));
+			String unit = matcher.group(2);
+
+			switch (unit) {
+				case "g":
+					return new Weight(amount);
+				case "kg":
+					return new Weight(amount * 1_000);
+				case "t":
+					return new Weight(amount * 1_000 * 1_000);
+				default:
+					throw new IllegalArgumentException(String.format("invalid weight unit %s", unit));
+			}
+		}
+		throw new IllegalArgumentException(String.format("invalid weight string %s", string));
+	}
+
+	public long getGrams() {
+		return grams;
+	}
+}
diff --git a/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/WeightConverter.java b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/WeightConverter.java
new file mode 100644
index 0000000..9dd2d81
--- /dev/null
+++ b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/mail/WeightConverter.java
@@ -0,0 +1,12 @@
+package io.reflectoring.configuration.mail;
+
+import org.springframework.core.convert.converter.Converter;
+
+class WeightConverter implements Converter<String, Weight> {
+
+	@Override
+	public Weight convert(String source) {
+		return Weight.fromString(source);
+	}
+
+}
diff --git a/spring-boot/configuration/src/main/java/io/reflectoring/configuration/unknownandinvalidfield/UnkownAndInvalidFieldProperties.java b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/unknownandinvalidfield/UnkownAndInvalidFieldProperties.java
new file mode 100644
index 0000000..27807c1
--- /dev/null
+++ b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/unknownandinvalidfield/UnkownAndInvalidFieldProperties.java
@@ -0,0 +1,22 @@
+package io.reflectoring.configuration.unknownandinvalidfield;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.stereotype.Component;
+
+@Component
+@ConfigurationProperties(
+        prefix = "myapp.unknown-and-invalid-field-module",
+        ignoreUnknownFields = false,
+        ignoreInvalidFields = true)
+class UnkownAndInvalidFieldProperties {
+
+  private Boolean enabled;
+
+  public Boolean getEnabled() {
+    return enabled;
+  }
+
+  public void setEnabled(Boolean enabled) {
+    this.enabled = enabled;
+  }
+}
diff --git a/spring-boot/configuration/src/main/java/io/reflectoring/configuration/unknownfield/UnkownFieldProperties.java b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/unknownfield/UnkownFieldProperties.java
new file mode 100644
index 0000000..84b5f52
--- /dev/null
+++ b/spring-boot/configuration/src/main/java/io/reflectoring/configuration/unknownfield/UnkownFieldProperties.java
@@ -0,0 +1,29 @@
+package io.reflectoring.configuration.unknownfield;
+
+import javax.validation.constraints.NotEmpty;
+import javax.validation.constraints.NotNull;
+
+import java.time.Duration;
+import java.util.List;
+
+import io.reflectoring.configuration.mail.Weight;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.boot.context.properties.DeprecatedConfigurationProperty;
+import org.springframework.stereotype.Component;
+import org.springframework.util.unit.DataSize;
+import org.springframework.validation.annotation.Validated;
+
+@Component
+@ConfigurationProperties(prefix = "myapp.unknownfield", ignoreUnknownFields = false)
+class UnkownFieldProperties {
+
+  private Boolean enabled = Boolean.TRUE;
+
+  public Boolean getEnabled() {
+    return enabled;
+  }
+
+  public void setEnabled(Boolean enabled) {
+    this.enabled = enabled;
+  }
+}
diff --git a/spring-boot/configuration/src/main/resources/application.properties b/spring-boot/configuration/src/main/resources/application.properties
new file mode 100644
index 0000000..a0d841e
--- /dev/null
+++ b/spring-boot/configuration/src/main/resources/application.properties
@@ -0,0 +1,8 @@
+myapp.mail.enabled=true
+myapp.mail.defaultSubject=hello
+myapp.mail.pauseBetweenMails=5s
+myapp.mail.maxAttachmentSize=1MB
+myapp.mail.smtpServers[0]=server1
+myapp.mail.smtpServers[1]=server2
+myapp.mail.maxAttachmentWeight=5kg
+myapp.mail.foo=foo
\ No newline at end of file
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/ConfigurationApplicationTests.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/ConfigurationApplicationTests.java
new file mode 100644
index 0000000..ffd3fba
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/ConfigurationApplicationTests.java
@@ -0,0 +1,16 @@
+package io.reflectoring.configuration;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest
+class ConfigurationApplicationTests {
+
+  @Test
+  void contextLoads() {
+  }
+
+}
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithAllProperties.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithAllProperties.java
new file mode 100644
index 0000000..b886086
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithAllProperties.java
@@ -0,0 +1,38 @@
+package io.reflectoring.configuration.mail;
+
+import java.time.Duration;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import org.springframework.util.unit.DataSize;
+import static org.assertj.core.api.Assertions.*;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest(properties = {
+		"myapp.mail.enabled=asd",
+		"myapp.mail.defaultSubject=hello",
+		"myapp.mail.pauseBetweenMails=5s",
+		"myapp.mail.maxAttachmentSize=1MB",
+		"myapp.mail.smtpServers[0]=server1",
+		"myapp.mail.smtpServers[1]=server2",
+		"myapp.mail.maxAttachmentWeight=5kg"
+})
+class MailModuleTestWithAllProperties {
+
+  @Autowired(required = false)
+  private MailModuleProperties mailModuleProperties;
+
+  @Test
+  void propertiesAreLoaded() {
+	assertThat(mailModuleProperties).isNotNull();
+	assertThat(mailModuleProperties.getDefaultSubject()).isEqualTo("hello");
+	assertThat(mailModuleProperties.getEnabled()).isTrue();
+	assertThat(mailModuleProperties.getPauseBetweenMails()).isEqualByComparingTo(Duration.ofSeconds(5));
+	assertThat(mailModuleProperties.getMaxAttachmentSize()).isEqualByComparingTo(DataSize.ofMegabytes(1));
+	assertThat(mailModuleProperties.getSmtpServers()).hasSize(2);
+	assertThat(mailModuleProperties.getMaxAttachmentWeight().getGrams()).isEqualTo(5000L);
+  }
+}
\ No newline at end of file
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithInvalidProperties.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithInvalidProperties.java
new file mode 100644
index 0000000..c5a2148
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithInvalidProperties.java
@@ -0,0 +1,25 @@
+package io.reflectoring.configuration.mail;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import static org.assertj.core.api.Assertions.*;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest(properties = {
+		"myapp.mail.defaultSubject="
+})
+@Disabled("this test will fail due to invalid properties")
+class MailModuleTestWithInvalidProperties {
+
+  @Autowired(required = false)
+  private MailModuleProperties mailModuleProperties;
+
+  @Test
+  void propertiesAreLoaded() {
+	assertThat(mailModuleProperties).isNotNull();
+  }
+}
\ No newline at end of file
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithUnknownField.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithUnknownField.java
new file mode 100644
index 0000000..b70b374
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/mail/MailModuleTestWithUnknownField.java
@@ -0,0 +1,22 @@
+package io.reflectoring.configuration.mail;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import static org.assertj.core.api.Assertions.*;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest
+class MailModuleTestWithUnknownField {
+
+  @Autowired(required = false)
+  private MailModuleProperties mailModuleProperties;
+
+  @Test
+  void propertiesAreLoaded() {
+	assertThat(mailModuleProperties).isNotNull();
+  }
+}
\ No newline at end of file
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownandinvalidfield/UnknownAndInvalidFieldModule.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownandinvalidfield/UnknownAndInvalidFieldModule.java
new file mode 100644
index 0000000..1722407
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownandinvalidfield/UnknownAndInvalidFieldModule.java
@@ -0,0 +1,9 @@
+package io.reflectoring.configuration.unknownandinvalidfield;
+
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+
+@SpringBootConfiguration
+@EnableConfigurationProperties(UnkownAndInvalidFieldProperties.class)
+class UnknownAndInvalidFieldModule {
+}
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownandinvalidfield/UnkownFieldPropertiesTest.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownandinvalidfield/UnkownFieldPropertiesTest.java
new file mode 100644
index 0000000..bc100a4
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownandinvalidfield/UnkownFieldPropertiesTest.java
@@ -0,0 +1,28 @@
+package io.reflectoring.configuration.unknownandinvalidfield;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import static org.assertj.core.api.Assertions.*;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest(properties = {
+		"myapp.unknown-and-invalid-field-module.unknown-property=foo"
+})
+class UnkownFieldPropertiesTest {
+
+	@Autowired(required = false)
+	private UnkownAndInvalidFieldProperties properties;
+
+	@Test
+	@Disabled("disabled due to unexpected behavior")
+	void loadsApplicationContext() {
+		// This test passes.
+		// However, I would expect this test to fail application context startup due to the unknown property.
+		// If we set ignoreInvalidFields to true, it works as expected.
+		assertThat(properties).isNotNull();
+	}
+}
\ No newline at end of file
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownfield/UnknownFieldModule.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownfield/UnknownFieldModule.java
new file mode 100644
index 0000000..e3c54b0
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownfield/UnknownFieldModule.java
@@ -0,0 +1,10 @@
+package io.reflectoring.configuration.unknownfield;
+
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Configuration;
+
+@SpringBootConfiguration
+@EnableConfigurationProperties(UnkownFieldProperties.class)
+class UnknownFieldModule {
+}
diff --git a/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownfield/UnkownFieldPropertiesTest.java b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownfield/UnkownFieldPropertiesTest.java
new file mode 100644
index 0000000..d4e3929
--- /dev/null
+++ b/spring-boot/configuration/src/test/java/io/reflectoring/configuration/unknownfield/UnkownFieldPropertiesTest.java
@@ -0,0 +1,25 @@
+package io.reflectoring.configuration.unknownfield;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import static org.assertj.core.api.Assertions.*;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest(properties = {
+		"myapp.unknownfield.unknown-property=foo"
+})
+@Disabled("this test is expected to fail due an unknown property")
+class UnkownFieldPropertiesTest {
+
+	@Autowired(required = false)
+	private UnkownFieldProperties properties;
+
+	@Test
+	void propertiesAreLoaded() {
+		assertThat(properties).isNotNull();
+	}
+}
\ No newline at end of file