Not receiving emails from Office 365 or Outlook.com users with MTA-STS configured on MIAB 0.50

Maintenance
1

Hi all,

Has anyone else had issues receiving emails from Office 365 or Outlook / Live Mail users when MTA-STS has been setup?

All tests I’ve run shows that my setup is good and I’m able to receive emails from GMail, GSuite Protonmail and other MTA-STS compliant email providers.

I can receive emails if I set the mode to “testing” in /var/lib/mailinabox/mta-sts.txt, but when I change back to “enforce”, no emails come in.

I get the below in the Office 365 Exchange message:

Reason: LED=450 4.4.317 Cannot connect to remote server [Message=451 4.4.8 MX hosts of ‘inoz.me’ failed MTA-STS validation.]

2

Just tried from outlook.com and e-mail come straight through.

Check your log for any clues perhaps …
lnav /var/log/mail.log

3

Thanks for checking and replying.

I’m not seeing anything in /var/log/mail.log as the TLS connection is not being established due to MS not trusting the connection with mode set to “enforce”

I’ve set a TLSRPT DNS record, which has Google sending me reports almost daily stating everything with my MTA-STS setup is happy, but no reports from Microsoft.

Uncle Google / DuckDuckGo doesn’t come up with much other than Microsoft recently implemented MTA-STS. I’m guessing either MS’s implementation may not be 100% correct, or, as my domain was recently using Office365 before moving back to MIAB, they may have some stale data about my domain hanging around.

4

Maybe get one of the throw away domain names being offered at discount for a yer(and then extortionate amount) add it to your MIAB and check if delivery is working.

I have decided to use a cheap domain for the primary/default domain name to make sure that something similar does not happen to me …

5

Thanks for the tip on the throw away domain. Best $1 I spent :wink:

In the end I resolved this by using MIAB as the primary DNS instead of setting up everything on external DNS providers due to the _mta-sts TXT record updating after config changes. I guess that record was out of sync, but the tests weren’t picking that up.