Make it build

.gitignore

@@ -1,3 +1,4 @@
 work/
 target/
+
 .idea/

pom.xml

@@ -34,6 +34,10 @@
     </dependencyManagement>
 
     <dependencies>
+        <dependency>
+            <groupId>io.jenkins.plugins</groupId>
+            <artifactId>javax-mail-api</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.jenkins-ci.plugins</groupId>
             <artifactId>mailer</artifactId>

src/main/java/io/jenkins/plugins/sample/NotifyByMailSecurityNotifierStrategyImpl.java

@@ -2,15 +2,15 @@
 
 import edu.umd.cs.findbugs.annotations.NonNull;
 import hudson.Extension;
+import jakarta.mail.internet.MimeMessage;
 import jenkins.plugins.mailer.tasks.MimeMessageBuilder;
 import org.jenkinsci.Symbol;
 import org.kohsuke.stapler.DataBoundConstructor;
 
-import javax.mail.Message;
-import javax.mail.MessagingException;
-import javax.mail.Transport;
-import javax.mail.internet.InternetAddress;
-import javax.mail.internet.MimeMessage;
+import jakarta.mail.Message;
+import jakarta.mail.MessagingException;
+import jakarta.mail.Transport;
+import jakarta.mail.internet.InternetAddress;
 import java.io.UnsupportedEncodingException;
 import java.util.logging.Level;
 import java.util.logging.Logger;