SendFailedException shown in log but not in the EMail Error Queue

Though the following error is recorded in the log file, there is no indication of a problem when looking at the EMail Error Queue.

2006-02-03 17:34:06,811 ERROR [atlassian.mail.queue.MailQueueImpl] Error occurred in sending e-mail: To='XXX@XXX' Subject='Created: (BRS-489) prod move: provide Discoverer access' From='null' FromName='Markus (JIRA)' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='null' MimeType='text/plain' Encoding='UTF-8' Multipart='null' MessageId='null'
com.atlassian.mail.MailException: javax.mail.SendFailedException: Invalid Addresses;
nested exception is:
class com.sun.mail.smtp.SMTPAddressFailedException: 550 5.7.1 Unable to relay for XXX@XXX

at com.atlassian.mail.server.impl.SMTPMailServerImpl.send(SMTPMailServerImpl.java:182)
at com.atlassian.mail.queue.SingleMailQueueItem.send(SingleMailQueueItem.java:47)
at com.atlassian.mail.queue.MailQueueImpl.sendBuffer(MailQueueImpl.java:68)
at com.atlassian.jira.service.services.mail.MailQueueService.run(MailQueueService.java:23)
at com.atlassian.jira.service.services.mail.MailQueueService.destroy(MailQueueService.java:43)
at com.atlassian.jira.service.JiraServiceContainer.destroy(JiraServiceContainer.java:82)
at com.atlassian.jira.upgrade.ConsistencyCheckImpl.destroy(ConsistencyCheckImpl.java:95)
at com.atlassian.jira.upgrade.ConsistencyLauncher.contextDestroyed(ConsistencyLauncher.java:33)
at org.apache.catalina.core.StandardContext.listenerStop(StandardContext.java:3710)
at org.apache.catalina.core.StandardContext.stop(StandardContext.java:4283)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1065)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1065)
at org.apache.catalina.core.StandardEngine.stop(StandardEngine.java:447)
at org.apache.catalina.core.StandardService.stop(StandardService.java:512)
at org.apache.catalina.core.StandardServer.stop(StandardServer.java:717)
at org.apache.catalina.startup.Catalina.stop(Catalina.java:586)
at org.apache.catalina.startup.Catalina.start(Catalina.java:561)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:271)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:409)
Caused by: javax.mail.SendFailedException: Invalid Addresses;
nested exception is:
class com.sun.mail.smtp.SMTPAddressFailedException: 550 5.7.1 Unable to relay for XXX@XXX

at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTransport.java:1130)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:525)
at javax.mail.Transport.send0(Transport.java:151)
at javax.mail.Transport.send(Transport.java:80)
at alt.javax.mail.TransportImpl.send(TransportImpl.java:18)
at com.atlassian.mail.server.impl.SMTPMailServerImpl.send(SMTPMailServerImpl.java:168)
... 22 more