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Mail problem: SCHEDULER-320 could not send mail (is 550 5.7.1 Unable to relay for ...)
The SMTP server fully rejects the mail address does not send mails to external addresses such as xxx@yyyyyy.com (i.e. addresses outside the company network) with the inforamtioninformation: 550 5.7.1 Unable to relay for xxx@yyyyyy.com ) and deletes mailrejects such mails. In addition, mails are not sent out to other recipients.
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If this does not work then ask your SMTP support why a mail with this address was deleted from the server. You can find more information about why a server deletes can reject a mail and give out this message on http://www.eudora.com/techsupport/kb/1593hq.html.