Forum Discussion
Exchange Online Protection SPF record
Hi, I have received a message sent via Exchange Online host IPv6 "2603:10a6:20b:c0::31". The message was marked as spam because of SPF fail. Subnet "2603:10a6:20b:c0::/64" is not in the list of O365 ...
This issue might not be resolved by MS soon or ever, because their infrastructure is huge and with a lot of moving parts. I did not get any help from MS365 support, because the issue is so hard to reproduce. Something you can do is activating DKIM signing for sending domains so that your messages could pass authentication despite issues with SPF.
I've come across the same issue. Many of my coworkers are using an old version of Outlook which sends mail through smtp.office365.com. Apparently this server uses IP addresses starting with 2603:10b6. However none of these servers are included with
"v=spf1 include:secureserver.net ~all"
So all their mail fails spf and gets flagged. Going through these servers also does not use the DKIM I set up. However if we use the web based email the servers used pass SPF and DKIM is used.
I wish MS would add all the correct IP's to their secureserver.net.
