SMTP error from remote mail server after pipelined MAIL 550 5.7.1

Rodney Ford

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Apr 22, 2019
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Hello all,
First post here!

Pretty inexperienced IT guy investigating some email errors we're getting.

Currently all email from our domain are rejected from @Hotmail @outlook addresses along with this error:

host hotmail-com.olc.protection.outlook.com [104.47.14.33]
SMTP error from remote mail server after pipelined MAIL FROM:<[email protected]______.com> SIZE=5148:
550 5.7.1 Unfortunately, messages from [__.__.___.___] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140)

Is this an issue we can correct on our end or do we just need to contact Microsoft (which I did days ago with no reply...) and get off their blacklist?

Any help is much appreciated!

Thanks in advance.
 
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GOT

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Yes, only they can remove you from their block list, and it may not even be your IP, based on the message, they could be blocking an entire subnet due to problems with other servers with similar IPs.

If you can get a second IP), idealling in a different class C, you could change the mail sending IP. Or you could use a service like Mailchannels which you would route email to instead of directly to the recipient system which in most cases mitigates the block.
 
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cPanelLauren

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Definitely an issue with your provider, an IP or range of IP's that they use is being blocked and you're not going to be able to unblock it.

If they're unwilling/unable to fix the issue something like mailchannels would work as @GOT suggested or you could host the mail remotely/elsewhere but it's the same concept.
 

unigen

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Mar 8, 2015
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I faced a similar issue with hotmail blocking one of my servers. I send an email requesting them to unblock. 2 days later it was done.

Have to make sure no one on your server is sending bulk mail or MS will block the IP.