Email Deliverability Issues to Outlook from AWS

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I'm encountering a persistent issue with email deliverability from my server hosted on AWS. Emails sent to Outlook users are being blocked with the following error message:

Error: 550 5.7.1 Unfortunately, messages from [my_IP_address] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140).

Here's what I've done so far:

Checked and updated my SPF and DMARC records to ensure they are correctly configured. Ensured my IP address is not on any blacklists. Changed the IP address of my server on AWS to rule out specific IP-related issues. Despite these efforts, the blocking issue persists. This is having a significant impact on my business operations, and it seems to be an issue that is out of my direct control and possibly related to the AWS network.

Has anyone else experienced this problem? Any advice on how I might resolve it? Also, are there specific steps AWS needs to take to assist in resolving these Outlook blocks?

I would appreciate any guidance or assistance the community can offer, and I would also be interested in hearing from an AWS representative if they have any suggestions for addressing this matter.

Thank you in advance for your help.

1 Answer
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I assume you have implemented the measures listed at How do I remove the restriction on port 25 from my Amazon EC2 instance or Lambda function?.

As per the error message

Error: 550 5.7.1 Unfortunately, messages from [my_IP_address] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140).

You EC2 IP is being blocked by receiving email server. Some companies may block emails from all EC2 IP addresses at part of their corporate security policy. Hence, changing of EC2 IP does not help. You will have to reach out to the organisation's security team to allow-list your EC2 IP.

Alternatively, you can explore using Amazon SES to send email. It supports SMTP interface. Under Pricing page, it states Free tier customers receive up to 3,000 message charges free each month for the first 12 months after you start using SES. Do check Free Tier page for any updates on SES usage

AWS
Mike_L
answered 19 days ago
  • Good thanks for your answer, but with the aws SES service I can't do the mail forwarding without verifying the account that sends me the mail and this is necessary for my business. So I need to get outlook to verify my account.

  • Thanks for the information. Since SES supports SMTP, perhaps add SES as additional profile to your Outlook. Receive email in your Outlook, and use SES profile to send out the email. Alternatively, you may want to consider using Amazon WorkMail for hosting your email.

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