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<p>I have deployed Hybrid environment for a customer who have Exchange 2010 SP3 with over 11K users. the customer was using SMTP gateway for spam protection and didn’t want to disable or close the gateway through the hybrid environment deployment or after and wanted to have their gateway constantly.</p>
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<p>While Microsoft doesn’t support any SMTP gateways in Hybrid environment I had to find a way to configure this gateway to allow any incoming or outgoing emails from Office 365 tenant to Exchange on-premises using the white list feature in all its services e.g. (Anti-Spam, Virus, spoof…etc</p>



<p>After configuring the hybrid deployment, I had a problem with mail flow from/to Exchange Online.</p>



<p>I have checked all Microsoft’s Office 365/Exchange Online/ Exchange Online protection IPs/CIDs in order to white list them or add them to the ignore list on the SMTP gateway in order for mail flow to not be checked from and to Exchange online if the source is Exchange on-premises but that didn’t work until I find a Microsoft article that which was modified very recently by Microsoft 31-05-2016.</p>



<figure class="wp-block-image"><a href="http://www.google.com/url?q=http%3A%2F%2Fwww.moh10ly.website%2Fwp-content%2Fuploads%2F2016%2F06%2Fimage.png&;sa=D&;sntz=1&;usg=AFQjCNGEIXbZeBV2Dw7XbMBq1C691i-HXA" target="_blank" rel="noreferrer noopener"><img src="https://lh5.googleusercontent.com/Q_gKuGMyghX_PjFvqHchrb-xt2nuRDxu9OskC0zG0uzsgYTkelaIJDB8jzBbrG4pN6QUut6o0LNOnWgepecxWlOrUt8cnioNR0fBB1wmwlUAICHi1t4=w271" alt="image"/></a> 

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<p>Click <a href="https://www.google.com/url?q=https%3A%2F%2Ftechnet.microsoft.com%2Fen-us%2Flibrary%2Fdn163581%28v%3Dexchg.150%29.aspx&;sa=D&;sntz=1&;usg=AFQjCNHkOGDYF1nQmjWCPnRLwgr4xhvoig" target="_blank" rel="noreferrer noopener">here</a> for the link</p>



<p>The article mentioned that the IP list have been updated, including the removed IPs list as well.</p>



<figure class="wp-block-image"><a href="http://www.google.com/url?q=http%3A%2F%2Fwww.moh10ly.website%2Fwp-content%2Fuploads%2F2016%2F06%2Fimage-1.png&;sa=D&;sntz=1&;usg=AFQjCNFHcWn-sswQdirEMT2pT1hSb_cQ4Q" target="_blank" rel="noreferrer noopener"><img src="https://lh6.googleusercontent.com/164ETjqze6sunCXFziEE3HgnA4HZE8cH9lDOBeOnPDdm-5qSXwHJX0RIH63jCBpNl9ajZ3EAOmfsK7Cr9erqvIeErdSMUEIooIdcZmJ6oAoMHsL67Po=w874" alt="image"/></a></figure>



<p>While tracing the logs on Office 365 Message tracer tool I noticed that the connection to the SMTP gateway has been refused due to an IP which the MS article described as “Removed” but it was still used to send emails from Exchange online.</p>
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<p>The IP was 213.199.154.78 was greylisted on the SMTP gateway due to it not being added to the white list.</p>



<figure class="wp-block-image"><a href="http://www.google.com/url?q=http%3A%2F%2Fwww.moh10ly.website%2Fwp-content%2Fuploads%2F2016%2F06%2Fimage-2.png&;sa=D&;sntz=1&;usg=AFQjCNHpZ4RIn3RpIVKIQAgJCMlyyWn-MQ" target="_blank" rel="noreferrer noopener"><img src="https://lh6.googleusercontent.com/1DDV1_z1oXHCa4X4Ju17k1gteV1Kjv6inwd0NmnHnHXqOivltae8D4QZ0K26e2RYkP6EY9lQiqulcMgaUDmkaT7ChxAYPypmpWzMsF5oVHefLe3LvXs=w673" alt="image"/></a></figure>



<p>If you read the article you’ll notice that the subnet 213.199.154.0 has been mentioned as removed. so adding the IP to the white list has solved the problem for me</p>



<figure class="wp-block-image"><a href="http://www.google.com/url?q=http%3A%2F%2Fwww.moh10ly.website%2Fwp-content%2Fuploads%2F2016%2F06%2Fimage-3.png&;sa=D&;sntz=1&;usg=AFQjCNFabMCh014yuBawoNvcIF1z1_f8kQ" target="_blank" rel="noreferrer noopener"><img src="https://lh3.googleusercontent.com/sQFp538gIQSCroaiJL3R-MWd_dZjdvqp8S09jhiLcUJlC4Z7bcBjqnJ9LqxdTv2xVOGXiAgV19YG9J9xrxJoWZWkua-I13Htu-S8bIJQAa8PMQmrG4jS=w673" alt="image"/></a></figure>



<p>REF:</p>



<p><a href="https://technet.microsoft.com/en-us/library/dn163581(v=exchg.150).aspx">https://technet.microsoft.com/en-us/library/dn163581(v=exchg.150).aspx</a></p>



<p><a href="https://technet.microsoft.com/library/dn163583(v=exchg.150).aspx">https://technet.microsoft.com/library/dn163583(v=exchg.150).aspx</a></p>



<p>Hope this helps</p>
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<p>For any questions or inquery please mail me <a href="mailto:info@moh10ly.com" target="_blank" rel="noreferrer noopener"><strong>info@moh10ly.com</strong></a></p>

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