Forum Discussion
Failed to send emails to outlook/hotmail recipients, returns error 550 5.7.515
We are supporting vendor of a public service, the system sends email notifications to patrons every day. The volume is around 20000-25000 emails per day. Recently, our mail server got large amount of bounced back emails (around 25%) that were not able to deliver to patrons with hotmail/outlook/live/msn email account.
From the returned "Diagnostic-Code: smtp;550 5.7.515", understand that it's because of the requirement of SPF (Pass), DKIM (Fail) and DMARC (Pass) authentication. However, currently our email infrastructure can't support the change of DKIM configuration. Can we request Microsoft to add our domain in whitelist and allow us to send emails to notify our patrons? Any way to contact hotmail/outlook/live/msn postmaster?
Please advise, thanks.
5 Replies
"Can we request Microsoft to add our domain in whitelist and allow us to send emails to notify our patrons? Any way to contact hotmail/outlook/live/msn postmaster?"
Answer: No, those are not customizable for DNS records. You could add this record to your SPF and that might help for some of the accounts. +include:spf.protection.outlook.com
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!
-- Recently, our mail server got large amount of bounced back emails
As far as I know the new mass mailer policy was put in place April 2025. Not sure why you are just now seeing the impact.
-- that it's because of the requirement of SPF (Pass), DKIM (Fail) and DMARC (Pass) authentication
Part of High Volume Policy and also in Anti-phishing policies
https://learn.microsoft.com/en-us/defender-office-365/anti-phishing-policies-about
-- Any way to contact hotmail/outlook/live/msn postmaster?
https://substrate.office.com/ip-domain-management-snds/postmaster/
Help needed too with the 550 5.7.515 error. Received a message from my meanwhile previous provider that my mail-account was used to send spam, that a 'problem' occured with their server and a 'corrupted' backup. All happened without my knowledge.
Moved to another provider. Problem seems solved. I can send to personal Microsoft accounts again for example. But business clients that have hosted their e-mail at Microsoft still can't receive my mail although my new provider says that they are delivered.
An error message isn't received anymore. Putting my account on the 'safe mail' list doesn't help (as read in the article above).
We're groping in the dark now; does someone have an answer?
Lots of thanks in advance!
