Incoming emails going to trash (no rules set) Lots of incoming mails skip the inbox and go directly to the trash folder (not the junk folder). When I visit my Trash folder I see a huge number of unread messages from legit senders.

I have Mail.app linked to my Exchange account for work (this is the only linked account).
Messages I send myself via my work's SMTP server always go to trash.
Incoming messages that I manually flag as Junk sometimes go to the Junk folder, and sometimes they show up in the Inbox, but they never go to the Trash folder.
I have no rules of any kind set up in Mail.app, and I never did.

My question is, who is the culprit - Mail.app, Exchange, or my work's SMTP server?
How do I find out?
As mentioned in a comment by @negacao another way to view mailbox rules is to use the webapp:
Webapp -&gt; Gear Icon -&gt; Options -&gt; Organize Mail -&gt; Inbox Rules

There was, in fact, a rule set there which I had completely forgotten about. Disabling the rule allows messages to come to the inbox from the SMTP server, which indicates this was the root of the problem.
This same rule is not visible anywhere within Mail.app, for some reason.
The moral of the story for me is, &quot;when in doubt, check the webapp&quot;.