I'm having some problems with an email server I manage delivering emails to Outlook / Hotmail and am trying to work out what is going on here. The email server is on the domains SPF list (and passes SPF) but doesn't have DKIM / DMARC configured.
I see the server "delivers" the mail successfully:
May 24 13:59:20 ironhide postfix/smtp: 93F7C1FCA8: to=<*****@outlook.com>, relay=outlook-com.olc.protection.outlook.com[188.8.131.52]:25, delay=1.3, delays=0.01/0.01/0.47/0.87, dsn=2.6.0, status=sent (250 2.6.0 <firstname.lastname@example.org> [InternalId=6425271132094, Hostname=CO1NAM04HT227.eop-NAM04.prod.protection.outlook.com] 7427 bytes in 0.408, 17.736 KB/sec Queued mail for delivery) May 24 13:59:20 ironhide postfix/qmgr: 93F7C1FCA8: removed
However, this email never comes through to the users inbox or junk folder. It is a little harder to diagnose since the email is accepted for delivery and removed from the postfix queue on the server.
Every other domain is totally fine (Gmail, Yahoo etc) and accepts mail. I've checked both the IPv4 + IPv6 addresses on the server but it is not blacklisted anywhere.
Any ideas? Also, since this email server handles 1000's of emails per day it is rather difficult / expensive to use a smarthost before anyone suggests it.