550 5.1.0 : Sender address rejected: User unknown in relay recipient table

I’m trying to get my Drupal 6.x site to send emails using the SMTP Authentication module. I have it fine working on other sites, and the site I’m having trouble with will actually send an email form the contact form, but when I try to register a new user, or even send a test email from the SMTP configuration page, I get this error message: 550 5.1.0 : Sender address rejected: User unknown in relay recipient table, along with a bunch of other garble.

Any ideas web rockers?

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Alex Schenker

If that doesn’t fix your issue, check the “enable debugging” box in the SMTP configuration settings, and send us the results for analysis (or pick out non-sensitive information and share it here in the forum). Remember to uncheck the debugging box when you’re done, or you will see a whole lot of code spit out every time your website tries to send an email.

Alex Schenker
The User unknown in relay recipient table means their is a mismatch of email addresses somewhere (ie. the sender is different than the email address you entered in the “from” field, or something similar). Email authentication has gotten stricter to ensure that email addresses aren’t being spoofed (faked), a technique commonly used by spammers.

In your Drupal case, try navigating to Site Configuration > Site Information (located at /admin/settings/site-information in Drupal 6.x), and make sure the email address there is the same as the one you use for SMTP authentication. If it’s different, make sure they’re both the same, and using the same email address you have registered to authenticate emails with your email hosting provider.