I keep getting these bounce backs, works on any other domain gmail, yahoo but not outlook/hotmail. is it me or them? I am using Smartermail with all possible settings setup ie DKIM SPF ii basically get a perfect score on https://www.mail-tester.com/web-zorml
Could not deliver message to the following recipient(s):
Failed Recipient: xxxxxxxxxxxxxxxxxxxxxx
Reason: Remote host said: 501 5.5.4 Invalid domain name [DB5EUR03FT018.eop-
EUR03.prod.protection.outlook.com]
prod.protection.outlook.com is Outlook/Microsoft's anti-snooping service. In case you didn't know, by viewing an email header, you can see the sender's IP. In order to circumvent this, Microsoft/Outlook sends your emails to prod.protection.outlook.com and then to the recipient, so if someone views the header, they get prod.protection.outlook.com's IP instead of yours. My guess is that your email provider doesn't recognise prod.protection.outlook.com as a valid domain name and thus can't send the email.