MailServer Administration and SMTP Auth

I ve setup my mail server in crowd as i ve also done it in JIRA and other systems. Even though i definitely supplied the right "username" and "password" for logging into the mailserver or better to be able to relay messages, i am always getting:

nested exception is:
com.sun.mail.smtp.SMTPAddressFailedException: 554 5.7.1 <xxxxx@xxxx.com>: Relay access denied

at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTransport.java:1196)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:584)
at javax.mail.Transport.send0(Transport.java:169)
at javax.mail.Transport.send(Transport.java:98)
at com.atlassian.crowd.manager.mail.MailManagerImpl.sendEmail(MailManagerImpl.java:69)

This exception normally appears when the client wasnt able to identify itself. Can it be that there is a problem with SMTP-Auth and Crowd?