550 Mailbox Unavailable Errors on Incoming Mail

[Theodore Long]

Some of our domains are facing issues in sending mail to our domain on our SBS 2003 Server with Exchange 2003 SP1. We get an error message saying " 550 Mailbox Unavailable Errors" on Incoming Mail. I am not able to make out the cause of this issue as both use Outlook Express. Is there anyone who can help me out dealing with this error??? I need to fix it as soon as possible.

[Allanoo]

I don't think there might be anything wrong with your server instead your Exchange might not be hosting fpmt.org's mail directly.

[unidentified]

Our SBS server is hosting fpmt.org mail. mail.fpmt.org and your MX record is: 10 mail.fpmt.org. [TTL=3601] IP=70.103.203.75 [TTL=3601] [US]. As far as i am aware the IP address is correct and we do get mails form other domains. This issue is specific with some of our domains only.

What else might cause this issue???

I am just running out of ideas. In my case i am using WatchGuard Firebox SMTP Proxy service and i am just running out of ideas. Any further help regrading this will be highly appreciated, thanks in advance.

[Techguru01]

Can you try bypassing the SMTP filter in Watchguard ? If yes, then you can do that and check out if the document mentions any specific error. If it does, then you can post it in your next reply so that i can have better idea of your environment and will try to find appropriate solution for fixing it.

[Hockson]

I have tried bypassing the SMTP filter in Watchguard and i have below unspecific error in the document

"These recipients of your message have been processed by the mail server:to someone at domain@fpmt.org; Failed; 5.3.0 (other or undefined mail
system status)
Remote MTA mail.fpmt.org: network error - SMTP protocol diagnostic:
550 Requested action not taken: mailbox unavailable"

I am not able to make out anything from this error. Do you?