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Hope someone can help me with the situation I am dealing with. Currently we have a mixed system for Exchange. We have 2 Exchange 2013 servers both running on Server 2012, and one user currently on Office 365. About half of the emails coming into our domain are delayed anywhere from 10 minutes to 6 hours. Outbound emails are flowing without any issues. The emails that are getting delayed are from no specific sender. I have been monitoring the message trace on outlook.com and the emails that are delayed mostly are given the reasons: 451 4.7.0 Timeout waiting for client input or 451 4.4.0 SMTPSEND.SuspiciousRemoteServerError. I have been on the phone with Microsoft and they say its our fault or the sender's fault. I have been searching the internet for a solution and so far no fix has done it. If you need any more information let me know. Thanks All!

FYI I am working on getting CU9 installed on the servers tonight. We'll see if that fixes the issue?

br13
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  • I'm not understanding the problem. The emails are delayed in reaching your server or they're delayed in being delivered to the mailbox after reaching your server? If the former, there isn't anything you can do about it. – joeqwerty Aug 18 '15 at 20:36
  • Some ISP scan mail when it's sent via their smarthost to prevent spam abuse, this check make the delay. You could check if the ISP is the same for those remote sender, else like joeqwerty's told, you can do nothing. – yagmoth555 Aug 18 '15 at 20:43
  • The emails are delayed in reaching the server. They reach outlook.com but about half of them are being delayed in reaching the server in my datacenter. Its quite random on which emails are getting delayed. Sometimes mail will flow, and email gets delayed and mail will still flow after that email. I have done the back-pressure checks but that showed nothing. – br13 Aug 19 '15 at 11:11

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