Environment:

Apple Mail v16.0 (3774.300.61.1.2)

MacBook Air w/ M1 chip

macOS v14.2.1 (23C71) "Sonoma"

Background:

-- I access several email accounts via POP to download/receive incoming messages; I upload/send via SMTP.  I do this for several different personal/management reasons.

-- I also use POP/SMTP configurations on iPhones & iPads, all of which are running the Mail app (v4+?) on iOS v15.7.

-- I am not experiencing any problems on the iOS devices.

-- I've been running this configuration for years without any significant issues.

-- On 01/09/24, I experienced the problem described below where mail stopped downloading.  I moved all of my emails from my inbox, sent, junk & trash folders to temporary storage; deleted my @zoho account and reinstalled it.  This did not resolve the problem; however, on 01/11/24, mail started downloading again.

CURRENT ISSUE:

-- @Zoho POP mail has stopped downloading to my MacBook Air.  (POP messages *are* downloading to my iPhones & iPads via Apple's iOS mail app.)

-- When I use Apple Mail's "Connection Doctor" and "Get Account Info" tools, both tell me the @zoho account is active and working; Apple Mail is communicating properly with the POP servers.

-- Apple Mail's "Get Account Info" shows all of the messages incoming on the @zoho account's POP server; I can confirm these are correct by logging into webmail and see all of the messages that aren't downloading.

-- There doesn't appear to be a message that is "blocking" the server/path.  @Zoho's "Unblock Me" tool indicates there are no blocks on my account, and the messages on the server that have not been delivered all are typical messages that I regularly receive.

-- When this happened earlier this month, I deleted the Apple Library files that regulate POP mail delivery (so messages aren't downloaded more than once); this didn't help.  I also deleted the @zoho account and reinstalled it; that didn't help, either.

-- When this happened earlier this month, I had a MacOS update that I hadn't installed.  I installed it, and I am now current.

Because my iOS devices are downloading POP messages correctly and the problem is limited to the MacBook Air, my first suspicion was that the problem is with the computer; however, I am not having problems with any of my other email accounts/providers, and the iOS and macOS interfaces are different (i.e., a problem on one wouldn't necessarily be duplicated on the other).

Posting here because I can't be the only person on the planet having this difficulty.  Hoping someone else can offer a solution.