Email dies after a long inactivity period

2025-01-21 18:51:08,530 [pool-1-thread-460] ERROR definitivequesting.api.SignupApiImplementation - failed to send signup mail to *****
java.lang.RuntimeException: org.eclipse.angus.mail.smtp.SMTPSendFailedException: 421 Timeout - closing connection

        at definitivequesting.api.mail.JakartaMailSender.send(JakartaMailSender.java:96)
        at definitivequesting.api.SignupApiImplementation.prepareSignup3SendMail(SignupApiImplementation.java:155)
        at definitivequesting.api.SignupApiImplementation.lambda$prepareSignup2InsertRecord$1(SignupApiImplementation.java:141)
        at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:859)
        at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:837)
        at java.base/java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:478)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: org.eclipse.angus.mail.smtp.SMTPSendFailedException: 421 Timeout - closing connection

        at org.eclipse.angus.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2407)
        at org.eclipse.angus.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:1812)
        at org.eclipse.angus.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1290)
        at definitivequesting.api.mail.JakartaMailSender.send(JakartaMailSender.java:81)
        ... 8 common frames omitted