Forum Discussion
Failed to send emails to outlook/hotmail recipients, returns error 550 5.7.515
Microsoft generally won’t whitelist domains that fail authentication. Services like Outlook.com and Hotmail require proper SPF, DKIM, and DMARC checks, so if DKIM is failing the emails can be rejected with the 550 error.
You can try contacting Microsoft Sender Support, but in most cases the real fix is enabling DKIM or sending through a mail service that supports it.
Thank your very-very much Rogerreed!
Found a solution by following your suggestion to contact Microsoft Sender Support.
First search result for 'Microsoft Sender Support' was the Microsoft page: Sender Support in Outlook.com
https://support.microsoft.com/en-us/office/sender-support-in-outlook-com-05875e8d-1950-4d89-a5c3-adc355d0d652
'Improve your spam reputation'
Followed the first step:
If you are running anti-virus software, check for the setting Internet Email Auto Protect or Internet Email Protection. If this setting is enabled, disable it and try sending a test message again.
Searched how to do that and followed one of the methods mentioned by AI based on:
https://support.microsoft.com/en-us/topic/information-about-the-attachment-manager-in-microsoft-windows-c48a4dcd-8de5-2af5-ee9b-cd795ae42738#:~:text=You%20may%20receive%20a%20Virus,exe%2C%20and%20then%20press%20Enter.&text=If%20you%20do%20not%20see,file%20that%20you%20failed%20before.
Made the new key 'Attachements' and set the value to 3 (not to 1 = disable).
After a reboot (just for sure) I can send e-mails to Microsoft hosted business accounts again.
Still a puzzle for me what this setting has to do with the problem experienced with outgoing mail. Don't know that much but most important for now it works again.And a lesson: forgot an important first step in the exclude analysis; try it on another device (my mobile phone e.g.). It would've given me the insight the problem was local.
Thank you very much once more and best-best regards!
