Mailserver does not deliver to certain email addresses

[andxclfor]

Using the built in SMTP, I have set up a mailing list with 10 external email addresses. All but two do receive the mails.

Of the two that do not, one is on @t-online and one is on @hotmail.com/@outlook.com. And both are the only ones on those two services.

Both do not get the mails at all, they are not in spam.

What am I doing wrong? Is there a way to trace the mails?

[jimcavoli]

At least for the hotmail/outlook addresses, you can check out SNDS - https://sendersupport.olc.protection.outlook.com/snds/index.aspx - to verify status and/or request unblocking if you're currently being blocked.

[moonmeister]

@andxclfor I've run into this as well. Though I get an undeliverable error usually. Basically, Microsoft uses a very broad blacklist that adds entire subnets to the list if there is one bad actor on the subnet. So I get blocked because someone else on DO is being bad.

[andxclfor]

@moonmeister Thank you. And what did you do? Change IP?

[andxclfor]

Turns out that my IP is spam. Taking it up with DigitalOcean.

Thank you all!

[ccfu]

@andxclfor IP reputation is becoming increasingly important for mail delivery and both T-Online and Microsoft have implemented quite aggressive checks. If your domain starts sending mail from a new IP, for example, there is a good chance it will initially be blocked. You should get an undeliverable error in such cases though. From experience I can say that T-Online have been very quick to rectify this.

[girish]

Sometimes the only way to overcome IP limitation is https://docs.cloudron.io/email/#relay-outbound-mails . But IIRC outlook atleast has a form you can fill up to get your IP/domain whitelisted (they send you an email that you have to click).

[moonmeister]

Just ran across this tool: https://www.mail-tester.com

Could be super helpful for folks.

https://answers.microsoft.com/en-us/outlook_com/forum/all/how-to-request-to-whitelist-a-domain-on-microsoft/3b6e2b4c-32e9-4e76-af38-dd0982e526b6

Has good info on solving Microsoft specific problems.

[humptydumpty]

The SNDS page/service is useless. It's good to tell if you're blocked or not and that's it. I signed up and added my server IP +8 months ago and I have yet to receive a single report from them. Anyway, I found the right page to apply for delisting if your IP is blocked: https://sender.office.com.

[andxclfor]

@humptydumpty thank you very much.

Here my result and their system reply:

The IP address in question is not currently blocked in our system. Please refer to the email message you received from Microsoft and follow the steps it suggests.

If you're trying to delist an IP address blocked in Hotmail.com/Live.com/Outlook.com, please use the following link.
https://support.microsoft.com/en-us/getsupport?oaspworkflow=start_1.0.0.0&LINK-EDITED

If you're trying to delist a banned or blocked sender, please open a support ticket from your tenant.

[andxclfor]

I end this thread because I now have a more specific one going.