Not all of our email is sending correctly.

Currently not all of our email is sending correctly. Some mail sends fine, other mail from certain domains gets hung up in the Exchange 2010 queue viewer for an extended period of time and eventually is sent. It seems that mail being sent to some domains gets hung up and other domains send fine! There seems to be no rhyme or reason to this? I get no events in the app or sys event viewer logs that I can see.

Thank you!
ImImInAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
In the Queue viewer you will see Last Error. When you are sending to one of these domains, does it show an error? You might also have to expand the column as well.

I would also check to make sure that you are not on any blacklists as well.

Will.
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ImImInAuthor Commented:
Thank you for your reply :-)

Last error:
451 4.4.0 Primary target IP address responded with 421 4.2.1 "Unable to connect". Attempted failover to alternative host, but that did not succeed. Either there are no alternative hosts or delivery failed to all alternative hosts.

As far as black listing goes, that is a very interesting question. 2 days ago when this problem first arose I checked the blacklists right away and we were not listed. Now it says we are listed with UCEPROTECTL3 !?!?
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ImImInAuthor Commented:
I was using MXToolbox to check for blacklisting. I checked it on Tuesday morning and we were not on the list. I was off yesterday and today I checked it again when you suggested blacklisting.  If you get blacklisted, doesn't that show up right away on tools like MXToolbox?  Is there a better tool(s) to use?
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Viral RathodConsultantCommented:
If you are facing issues where your outgoing Emails are consistently rejected by other servers or land up in Junk Email or SPAM folders of the recipient mail box, this test can help you in identifying the problems.

Testing Process

Send an Email to test@allaboutspam.com
That email will bounce with a URL in the bounce messge.
Either click on the URL or Copy/paste the URL in a browser.
You will see report on your Email Server.
 

Ref : http://www.allaboutspam.com/email-server-test/
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Will SzymkowskiSenior Solution ArchitectCommented:
451 4.4.0 Primary target IP address responded with 421 4.2.1 "Unable to connect". Attempted failover to alternative host, but that did not succeed

This is a common error message when you are in fact blacklisted or you are having Reverse DNS issues with your MX record. I would check that first and make sure that everything is good. If your Reverse Records are good then i would start to try and remove your domain from being blacklisted.

Very common error.

Will.
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ImImInAuthor Commented:
How does this explain the emails finally send after 12 hours or so and that is tis only affecting a handful of domains that we send to?
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ImImInAuthor Commented:
Also, this problem started happening after we changed web-hosts and changed DNS records to our domain registrar.
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