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I have setup an Exchange 2010 Server a couple months ago and it has been working great. Recently (last 2 weeks) we started getting NDR's on some of the email.

... Relaying denied. Please check your mail first or restart your mail session.

Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept e-mail from certain senders, or another restriction may be preventing delivery.

and

Firewall Error

A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.

I have not made any changes to the server besides Antispam updates and tweaking the Antispam settings (content filtering actions).

Anyone have any tips of where I could start looking? I was finding information about Receive Connectors possibly being the culprit. I just have the 2 default connectors going. Should I create new ones? If so, how would I create connectors that would suffice for us. (Exchange users and also OWA users.)

I can provide any other details anyone needs in order to help me out.

~Aeotrin

Update: The error I am getting back also looks something like this:

Mail.server.ofRecipient rejected your message to the following e-mail addresses:

Recipient Name (recipientEmail@company.com) (recipientEmail@company.com)

Mail.server.ofRecipient gave this error: ... Relaying denied. Please check your mail first or restart your mail session.

Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept e-mail from certain senders, or another restriction may be preventing delivery.

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Are the NDRs received when you send messages out or are they received by people trying to send to you? –  Phil Apr 11 '11 at 15:05
    
I receive them anywhere from 1-5 minutes after I send an email. The NDR does not happen everytime I email the contact though, which makes it even harder of a problem. –  Aeotrin Apr 11 '11 at 17:35

2 Answers 2

up vote 1 down vote accepted

Please check if you server isn't on blacklist http://www.mxtoolbox.com/blacklists.aspx

Also try https://www.testexchangeconnectivity.com/ some options to see if you can find any anomalies in your Exchange setup.

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Tried the mxtoolbox blacklist check, and its clear. 2 of them timeout but the rest are ok. –  Aeotrin Apr 11 '11 at 16:10
    
The Exchange Test for Outbound SMTP Test succeeded with warnings. Attempting to find the SPF record using a DNS TEXT record query. ExRCA wasn't able to find the SPF record. –  Aeotrin Apr 11 '11 at 16:17
    
Are NDR's for every single email you send or just a few? Can you try to telnet <some_mail_server> 25 port (of course related to the email you're sending to? You can use mxtooblbox.com to find out proper mail server to test. –  MadBoy Apr 11 '11 at 16:29
    
I had an email go through this morning, and 1 fail. I used telnet <> 25 to the mail server and tried this: ehlo rset mail from:myemailaddress@mail.com rcpt to:emailCausingNDR@mail.com and got this response: 550 5.7.1 Unable to relay –  Aeotrin Apr 11 '11 at 16:54
    
Depending on the Spam scoring for other companies, it could be blocking based on no SPF record. I've never set one of those up my self, but it looks like Microsoft has a walk through. Let me know if that works out for you. microsoft.com/mscorp/safety/content/technologies/senderid/… –  Nixphoe Apr 11 '11 at 17:02

First thing I would do is check your outgoing addresses and/or hostnames with the various anti-spam organizations. We mistakenly got on a blacklist once and this is pretty much what we saw.

Good luck getting off of it, we ended up going with a 3rd party delivery service to get past the crisis.

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