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SMTP Mail Erro

red_75116 asked
Medium Priority
Last Modified: 2012-05-06
I have a customer who has been trying to send us mail and gets an error back when he does.  He is getting Error Transferring to DOMAIN NAME: SMTP Protocol returned a permanent error 550 5.7.1 Unable to relay mail for user@domain.com.  The mail seems to be working fine and we get thousands of emails a day.  Is this a problem on their end and I don't need to worry.
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tigermattSite Reliability Engineer
Most Valuable Expert 2011


If you are receiving email just fine from external sources, then the issue is more than likely at the customer's end. An 'Unable to relay' error message would specifically indicate that they have some sort of email transmission issue.

If the customer were blocked from sending you email from your server, I'd expect a different message or indeed completely different behaviour. I don't think you have anything to worry about here.


I'd check the following to check to see if they are blacklisted, http://www.mxtoolbox.com/diagnostic.aspx and also http://dnsstuff.com.  They need to check that they have full forward and reverse DNS for their mail server's IP addresses.  Also, they need to verify their MX records in their DNS, is it pointed to the correct IP address for their mail server(s).  The error you indicated is one that is generated typically by a spam-filtering service (which could be a separate gateway or a filtering device).  

If everything passes their test then I would check your logs for any indications that your servers are refusing the messages and why.  You could also have them check the message header for further details on where the message is being sent.


thanks,  I ran the tools at mxtool box and it says - Does this look right?  I only care that mine is working and set correctly.  They "claim" they only get this message sending to us so I need to make sure I am setup ok.

 HELO please-read-policy.mxtoolbox.com
250 web143.discountasp.net Hello [ [62 ms]
MAIL FROM: <test@mxtoolbox.com>
250 2.1.0 test@mxtoolbox.com....Sender [62 ms]
RCPT TO: <test@mxtoolbox.com>
550 5.7.1 Unable to relay for test@mxtoolbox.c [78 ms]
221 2.0.0 web143.discountasp.net Service closing transmission chann [62 ms]

red 75116,
First, even if you are on a blacklist you should still receive email, so when they send to you you should be able to receive the email.  In the 6th line above it should indicate that you should be "Unable to relay"  Being able to relay means that your system is open and can be used to send out spam or other unwanted email via your server.  Make sure that you have checked for all of your your mail servers by going to the MX Lookup.  At this point I'd say that as long as you've verified that you aren't on any blacklist and you aren't having any other problems receiving email I'd say the problem is with the sender.  You should also check the following site for being blacklisted: http://cbl.abuseat.org/ And if you have any filtering devices on your network such as Ironport or and ASA firewall check that you don't have them listed.  
A mail server resonds with "Unable to relay" when it is being asked to relay e-mail for a domain that it doesn't handle and the sender does not have the permission to relay the message through the e-mail server instead of deliverying it to the e-mail server.

This means that the sender is not authenticating his or herself with his or her outgoing e-mail server, or that the message is being mistakenly delivered to the wrong server (to a server that doesn't actually handle e-mail for that domain). It's impossible to tell which is the issue without knowing which mail server gave the rejection message. The headers inside the bounce (delivery status notification) or the headers of the bounce should indicate which is the case.
From MXToolbox your results should show up like this:

RESULT: mail.jcmh.com
Banner:      220 intmail.xxxx.com ESMTP
Connect Time:       0 seconds - Good
Transaction Time:       0.234 seconds - Good
Relay Check:       OK - This server is not an open relay.
Rev DNS Check:       OK - resolves to mail.xxxx.com
GeoCode Info:      Geocoding server is unavailable
Session Transcript:      HELO please-read-policy.mxtoolbox.com
250 intmail.xxxx.c [47 ms]
MAIL FROM: <test@mxtoolbox.com>
250 sender <test@mxtoolbox.com> [62 ms]
RCPT TO: <test@mxtoolbox.com>
550 #5.1.0 Address rejecte [62 ms]
221 intmail.xxxx.c [62 ms]

Obiously the times in ms will \ can be differentYou can also use the Analysis Header on their site to check the information in the header of an email if you aren't certain what it means.  Hope this helps.

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