mail

Thank you for your reply, and info. that surely rules out needing to try an update.

Re: Incoming mail sometimes goes to the wrong inbox

You might want to check the inbox folder names, and the inbox file structure.

Eg:

(NB: Above is on macOS Monterey 12.6.3 and is working ok.)

or

Here's an Apple's article for Ventura 13.2

Read emails in Mail on Mac – Apple Support

Eg: says you can:

"Change which emails are shown"

and

"Change how emails are shown"

Hi sjs72,

Wondering which iMac model you are using, and which MacOS is installed.

Seems we would mostly have just the one folder named "All Inboxes", and within that folder, folders named for each Mail provider (Eg: Yahoo, Google, etc.)

(For older Mac OS versions, the file structure / Mail app / may be different.)

Why is this happening?

There could be a variety of possible reasons, so, likely could not guess the one correct one for your case.

Eg:

If you have a different Inbox file structure, or extra Inbox folders, perhaps incoming Mail from providers could end up in an incorrect box, because of the file structure, and folder names not matching the expected structure.

or

Perhaps updating to the newest MacOS compatible with your iMac would help put things in order.

All the best :-)