bug: mailgun failed to deliver some messages to outlook

[xiaohanyu]

Description

We got some logs from mailgun showing that it fails to deliver the verification code mail to users:

The error log:

5.7.1 Unfortunately, messages from [198.61.254.59] 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. [Name=Protocol Filter Agent][AGT=PFA][MxId=11B9CB3CBE70C55A] [DB3PEPF0000885D.eurprd02.prod.outlook.com 2024-10-07T11:48:34.472Z 08DCE59E609E592B]"

4.7.650 The mail server [69.72.42.6] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://postmaster.live.com (S775) [Name=Protocol Filter Agent][AGT=PFA][MxId=11B9A39F520F25FB] [AMS0EPF000001B0.eurprd05.prod.outlook.com 2024-10-07T11:32:37.217Z 08DCD1CFD0B7A9E3]

The root cause is still unknown but we need to deal with this. Mailgun shows that more than 10% mails are failed to deliver, which is a serious issue for user onboarding.

Recently our email delivery rate is 85%, which is very low.

To Reproduce

NA

Actual Behavior

Expected Behavior

• Email delivery should have 98% delivery rate.

[Optional] Screenshots

NA

Desktop

NA

Smartphone

NA

Additional Context

NA