Comments on: 550 5.7.1 Unable to relay http://itknowledgeexchange.techtarget.com/itanswers/550-571-unable-to-relay/ Thu, 23 May 2013 23:28:15 +0000 hourly 1 By: labnuke99 http://itknowledgeexchange.techtarget.com/itanswers/550-571-unable-to-relay/#comment-99508 labnuke99 Mon, 28 Nov 2011 17:57:57 +0000 #comment-99508 You may need to perform a packet capture between your mail server and one of the undeliverable email domains. Can you recreate the problem on demand? If so, setup Wireshark or some other packet capture tool so it can see what transactions the sending server has with the receiving server (include any traffic to/from the sending server so you can see DNS – MX record lookups and such). This may give some indication if the DNS lookup may be failing or there may be some rejection message coming from the receiving host.

Consider also checking disk and memory resources on your relay host. Look at the network utilization also to see if the capacity is used up by other services.

]]> By: exchstart http://itknowledgeexchange.techtarget.com/itanswers/550-571-unable-to-relay/#comment-99486 exchstart Mon, 28 Nov 2011 12:29:19 +0000 #comment-99486 Hi Labnuke,

Thanks for your response, as you said I have checked my DNS and cant find any issue in it and coming to my firewall I cant find any blocking for our SMTP relay .

Some of the details about this issue are,

1. This issue happens randomly for some domains and when i used ” Message Tracker” i found after “SMTP:started outbound TRanfer of Message” then it gives ” SMTP: Non delivery msg generated”

2. We are using a Frontend server for external mails so when I check the queue after sending the mail for a domain it will be clear and there will not be any mails stuck in that queue.

So i cant figure out where the exact issue and once I find that i can try to resolve it.

Please help me out to resove this if u can.

Thanks

Asif

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