2018-11-08 23:45:39,854 WARN  [mail-sender:thread-1]  c.a.s.i.mail.DefaultMailLogger 1 mail message not sent due to errors (0 sent successfully): see mail log for details
...
2018-11-08 23:58:53,626 WARN  [mail-sender:thread-1]  c.a.s.internal.mail.MailServiceImpl Pausing sending of emails for 5 seconds due to a previous error while sending

2018-11-08 04:17:44,851 ERROR [mail-sender:thread-1]  bitbucket.mail-log Sending mail failed. Please verify the mail server configuration and check the logs for details; recipient: user@domain.com@domain.com; subject: PROJ/REPO - Pull request #1289: My pull request
org.springframework.mail.MailParseException: Could not parse mail; nested exception is javax.mail.internet.AddressException: Domain contains illegal character in string ``user@domain.com@domain.com''
        at org.springframework.mail.javamail.MimeMailMessage.setTo(MimeMailMessage.java:111)
        at com.atlassian.stash.internal.mail.MailServiceImpl.lambda$newMimeMailMessagePreparator$2(MailServiceImpl.java:440)
        at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:359)
        at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:350)
        at com.atlassian.stash.internal.mail.MailServiceImpl.sendMessageSynchronously(MailServiceImpl.java:281)
        at com.atlassian.stash.internal.mail.MailServiceImpl.lambda$submit$0(MailServiceImpl.java:161)
        at com.atlassian.stash.internal.concurrent.DefaultTransferableStateManager$StateTransferringRunnable.run(DefaultTransferableStateManager.java:166)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.lang.Thread.run(Thread.java:748)
        ... 1 frame trimmed
Caused by: javax.mail.internet.AddressException: Domain contains illegal character
        at javax.mail.internet.InternetAddress.checkAddress(InternetAddress.java:1323)
        at javax.mail.internet.InternetAddress.parse(InternetAddress.java:1116)
        at javax.mail.internet.InternetAddress.parse(InternetAddress.java:655)
        at javax.mail.internet.InternetAddress.parse(InternetAddress.java:632)
        at org.springframework.mail.javamail.MimeMessageHelper.parseAddress(MimeMessageHelper.java:707)
        at org.springframework.mail.javamail.MimeMessageHelper.setTo(MimeMessageHelper.java:593)
        at org.springframework.mail.javamail.MimeMailMessage.setTo(MimeMailMessage.java:108)
        ... 11 common frames omitted