System Administrator - Undeliverable email

Curiosityx · 19 Feb 2009 at 16:15

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

Rob7865 · 19 Feb 2009 at 16:24

What is the Code on the NDR? There could be a number of reasons - the SMTP error number will give you a pointer.

Have you got your rDNS and PTR Records setup correctly, do you have a SPF record in place. Does the receipient have issues with their mailbox, is it over its set limits etc....

ttfn
Rob

Curiosityx · 19 Feb 2009 at 16:53

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>

Sin_Chase · 19 Feb 2009 at 18:11

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

oddjob62 · 19 Feb 2009 at 18:43

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

quackers · 19 Feb 2009 at 20:00

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

Curiosityx · 19 Feb 2009 at 20:10

Sin_Chase said:
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.

oddjob62 said:
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.

quackers said:
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.

quackers · 19 Feb 2009 at 22:03

If it's a reverse dns issue, you'll probably find mails stuck in the queue in exchange. Try this:

http://postmaster.aol.com/tools/rdns.html

You should get something like 192.168.0.2.bt.connect.com etc

Post what you get

svbooga · 19 Feb 2009 at 22:08

quackers said:
If it's a reverse dns issue, you'll probably find mails stuck in the queue in exchange. Try this:

http://postmaster.aol.com/tools/rdns.html

You should get something like 192.168.0.2.bt.connect.com etc

Post what you get

or this one if you dont know your public IP:- http://remote.12dt.com/

Sin_Chase · 19 Feb 2009 at 23:30

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

Shouldn't matter, they are still the front end mail receiver engines. They should accept a bog standard telnet on port 25 and SMTP commands.

s0ck · 21 Feb 2009 at 22:59

If it's not the PTR see if the recipients are using Exchange message filtering. We had this issue about 6 weeks back.