If a user signs up with an invalid e-mail address, and submits a new issue, then the "assigned to" user recieves an infinite set of e-mail notifications. This appears to be because the mail is first sent to the "assigned to", and then sent to the user who reported the bug. If the second send fails (when sending to the invalid user e-mail address), the mail is left in the mail queue, and then resent every minute. Stack trace is: javax.mail.SendFailedException: Sending failed; nested exception is: javax.mail.SendFailedException: Invalid Addresses; nested exception is: javax.mail.SendFailedException: 550 5.1.2 unknown host or domain: nate@$ at javax.mail.Transport.send0(Transport.java:219) at javax.mail.Transport.send(Transport.java:81) at alt.javax.mail.TransportImpl.send(TransportImpl.java:18) at com.atlassian.mail.server.impl.SMTPMailServerImpl.send(SMTPMailServe$ at com.atlassian.mail.MailFactory.sendEncodedMail(MailFactory.java:92) at com.atlassian.jira.mail.UserMailQueueItem.send(UserMailQueueItem.jav$ at com.atlassian.jira.mail.MailQueue.sendBuffer(MailQueue.java:60) at com.atlassian.jira.service.services.mail.MailQueueService.run(MailQu$ at com.atlassian.jira.service.JiraServiceContainer.run(JiraServiceConta$ at com.atlassian.jira.service.ServiceRunner.execute(ServiceRunner.java:$ at org.quartz.core.JobRunShell.run(JobRunShell.java:160) at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.$ rethrown as com.atlassian.mail.MailException: Sending failed; nested exception is: javax.mail.SendFailedException: Invalid Addresses; nested exception is: javax.mail.SendFailedException: 550 5.1.2 unknown host or domain: nate@$ at com.atlassian.mail.server.impl.SMTPMailServerImpl.send(SMTPMailServe$ at com.atlassian.mail.MailFactory.sendEncodedMail(MailFactory.java:92)