Email problems with Thunderbird

I have a strange problem when sending email to my cousin through Thunderbird. I get an error that says the user is unknown. However when I send him email through the Webmail interface or if I use my GMAIL account I have no problem. I have Thunderbird setup to go through my domain on Dreamhost.

Does anybody have any clue what could be the problem. I contacted Dreamhost about it, but they couldn’t seem to pinpoint the problem.

Please forgive me if my comment/suggestion sounds overly simple, or patronizing, as I do not know for sure from your post whether the “user” that is “unknown” is you or the addressee, and you did not indicate whether you are sucessfully sending mail to others using Thunderbird.

Having said that, one difference between sending via Thunderbird (imap or pop) and either the webmail interface or gmail, is the potential for confusion when “authenticating”.

Thunderbird pop or imap requires you identify yourself with your “m123455” user, not your “user name” as used in webmail or gmail.

If you are sucessfully sending email to any others using Thunderbird, then this obviously is not your problem, but if not, you might check that.

If you are only getting the errors when sending to one addressee, then I’m stumped!


The user is my cousin, or even his wife for that matter. They both have email addresses affiliated with his domain. I do successfully send/receive email with everybody else using Thunderbird.

One interesting note is that I think my cousin started using a spam filter shortly before I started having this problem. I think it is SpamAssassin. The program requires you to reply to his SpamAssassin filter, if you will, to authenticate yourself before he will accept emails from you.

Sounds like the problem isn’t really yours but your cousins – or at least it’s on his side and heS the one who has to fix something.

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