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SES emails blocked / bounced by all Microsoft (hotmail, Live, MSN, etc)

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I've been using SES for a while, email list about 6,000. Longstanding (years...all proper subscribers). Recently, I see everything going to Microsoft properties is bouncing, all of them have the same feedback for the bounce:

Bounced Reason: smtp; 550 5.7.1 Unfortunately, messages from [23.251.242.9] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [SN1NAM02FT0055.eop-nam02.prod.protection.outlook.com] @ 2022-07-14 22:48:37

I have no idea what to do. Any guidance?

1 Answers
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It may be best to open a support case (from the AWS console) so the AWS support team can help look at the logs to further assist.

I've seen this due to the fact that, by default, SES messages are sent from a shared pool of IP addresses, meaning you and other customers may be originating from the same AWS-owned IP block.

From the error you posted, it sound like that a set of IPs you've been using have been added to a third-party blocklist. The AWS SES team works to keep AWS IPs from being blocked, but it does occasionally happen. A support case can help highlight this to get resolution.

Alternatively, you can chose to use a dedicated pool of IP addresses, potentially avoiding being blocked due to others' activities.

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answered a month ago
  • I'm a small-time user. Longstanding email list for years of legit subscribers. The first thing I did was put in a ticket to AWS. Totally blew me off and referred me here. And you make a good point. I do not have dedicated IP, so this may have nothing to do with me.

    Zero stars for AWS support.

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