Error 550 5.4.300 and 421 4.4.2 when sending to aol.com email address

Question

I am getting message 550 5.4.300 and 421 4.4.2 when sending email to aol.com account. I checked with recipient and I am not on their blocked senders list.

I updated to windows 11 to see if that helped. no luck.

Answer 1

Based on your description, please kindly check if set up SPF, DKIM and DMARC for your custom domain in Microsoft 365 completely. Please also make sure if your network bypassed Office 365 URLs and IP address ranges which help to deliver email to aol account.

If all configurations are correct, and you only have this issue with AOL and Yahoo accounts, based my previous experience, this issue may be caused by that Yahoo had identified Microsoft as "abusive”. This is the issue between Yahoo and Microsoft, instead of your issue.

 Some similar thread:

All emails I am attempting to send to Yahoo/Aol accounts are bouncing - Microsoft Community

 You could contact Microsoft Support to report this issue: Get support - Microsoft 365 admin | Microsoft Learn

Or ask the administrator of your email domain to [submit a request to the AOL Postmaster support team](https://senders.yahooinc.com/contact/"Visit our help page to submit a Sender Support request."). Why can't I send mail to AOL Mail users? - AOL Help

 If this answer helps you please mark "Accept Answer" so other users can reference it.