SES Shared IP Blocked by Microsoft — Delivery Failure 550 5.7.1 (S3150)

Question

We are using Amazon SES (ap-south-1 region) with a shared IP pool to send transactional emails from hello@mypivot.work. We received a delivery failure (550 5.7.1) for a recipient at a Hotmail/Outlook address. The sending IP 76.223.180.43 is on Microsoft's blocklist (Error code: S3150). DKIM is properly configured for both amazonses.com and mypivot.work. Since we are on a shared IP pool, we cannot control which IP is used per send. Can AWS move us to a cleaner shared IP pool, or is a Dedicated IP the only permanent fix for reliable delivery to Hotmail/Outlook recipients?

Riku_Kobayashi · Answer

Hello.

To my knowledge, I've seen several cases where people use dedicated IP addresses to avoid problems like yours.  
Also, as described in the following document, using a dedicated IP address isolates you from the SES shared pool, allowing you to maintain your reputation as an email sender.  
Therefore, I think it will fit your use case.  
https://docs.aws.amazon.com/ses/latest/dg/dedicated-ip.html#dedicated-ip-managed-reputation  
> Dedicated IP addresses (standard)—after warmup, your IP addresses are isolated from the SES shared pool and you maintain your own sender reputation by sending consistent and predictable volumes of email.

By the way, you might be able to get your IP address unblocked by contacting Microsoft support, so you could try that as well.  
https://olcsupport.office.com/

Kyuseong_H · Answer

I recommend transitioning to a Dedicated IP for reliable email delivery to Hotmail/Outlook recipients. 
Please note that Dedicated IPs incur additional charges beyond the standard SES pricing.

If you have any additional questions or need further assistance, please feel free to reach out anytime.

Thank you.

SES Shared IP Blocked by Microsoft — Delivery Failure 550 5.7.1 (S3150)

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