System Administrator - Undeliverable email

[Curiosityx]

Greetings, as a company we seem to get a lot of "Undeliverable" emails, most of these i can check using SmtpDiag which comes back ok. The ones that fail we can receive email from said person but send back to the return address.

Ive gone through the SMTP virtual server, SMTP connector and Message Delivery all of which seem fine, personally i can send email without issue to a multitude of different people without issue. We are running 2003 SBS Sp2 and Exchange Sp2.

Could anyone recommend what could be the cause of this?

Regards

 

[Curiosityx]

All the errors are 550 related, these are three emails just from today. Only problem is know for a fact that these are valid recipients. We have an SPF record but our reverse DNS doesnt function correctly which im currently trying to address as i have a feeling that recipient mails servers performing reverse lookups will at present get a different host address.

The following recipient(s) could not be reached:

'[email protected]' on 19/02/2009 15:44
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<mail.falsedomain.co.uk #5.5.0 smtp;550 Unrouteable address>

The following recipient(s) could not be reached:

[email protected] on 19/02/2009 15:19
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<mail.falsedomain.co.uk #5.5.0 smtp;550 MAILBOX NOT FOUND>

The following recipient(s) could not be reached:

[email protected] on 19/02/2009 12:05
Could not deliver the message in the time limit specified. Please retry or contact your administrator.
<mail.falsedomain.co.uk #4.4.7>

 

[Curiosityx]

And its the recipients mail server that is giving you these SMTP error codes, not yours?

Indeed, would like to rule out my end completely.

HAve you tried sending using basic telnet. That way you can rule out your SBS Server being an issue

For some yes, others sit behind smart hosts or managed email providers such as messagelabs.

Of the mails that are being bounced back, are they to the same domain etc?

Try checkdns on each domain, they might be part of the same company/server etc

Ive been running all my checks through mxtoolbox.com and robtex.com to be sure, of course there is the odd email that has been miss spelt.


Ive gotton in touch with the people who manage our netblock to point to our DNS provider to perform reverse DNS resolution on our ip range.