Getting "dsn=5.0.0, stat=Service unavailable" when trying to send mail from sendmail through Exchange relay
Issue
- When trying to send email from sendmail via an Exchange relay, the following message is received on the logs:
Sep 25 13:21:53 hostname sendmail[7186]: s8PHLljD007186: to=<user@example.com>, delay=00:00:06, xdelay=00:00:06, mailer=relay, pri=33458, relay=node.outlook.com [X.X.X.X], dsn=5.0.0, stat=Service unavailable
Environment
- Red Hat Enterprise Linux 5
- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux 7
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
- Sendmail
- Exchange or Office365 mail relay
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