All incomming/outgoing emails end up in "junk" folder

[kamarya]

I have setup two domains lets say A.com and B.com. I have setup the mail server on A.com and it works fine (for whaterver is @A.com). For domain B.com I have set MX records to mx.A.com so A.com provides email services for both. For B.com I have made https://mta-sts.B.com/.well-known/mta-sts.txt with the following content:

mode: enforce
max_age: 604800
mx: mx.A.com

Why all incoming/outgoing emails to/from B.com end up in junk folder ? What am I missing ?

P.S. I use Mozilla Thunderbird as client

[foxcpp]

Can you check the header of messages sent to Junk and post the contents of Authorization-Results field? This may be caused by SPF/DKIM mismatch.

[kamarya]

I do not see anything failing in the header.

Authentication-Results: dkim=pass spf=pass

[foxcpp]

Then it must be something about recipient spam policy. You can try marking emails from B.com as "non-spam" in its UI, this might help.