How can I change the port used by a Mac Mail account?

I've added a new account via Mac Mail. The host uses port 993 for IMAP, and 543 for SMTP, with the same username and account for each. I unchecked "Automatically manage connection settings" and set that up, and Mac Mail has successfully connected to the SMTP server, but not the IMAP server. I have double- and triple- checked that the settings I entered are correct. I've also tried checking "Automatically manage connection settings". Checking the logs, in all cases, it's using port 143 for IMAP, ignoring what I've entered via the UI.

READ Apr 22 08:02:01.178 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:REDACTED -- port:143 -- socket:0x600012e11860 -- thread:0x600009fe3c00
7.614 NO [AUTHENTICATIONFAILED] Authentication failed.

WROTE Apr 22 08:02:01.179 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:REDACTED -- port:143 -- socket:0x600012e11860 -- thread:0x600009fe3c00
8.614 LOGIN USERNAME_REDACTED ********************

READ Apr 22 08:02:03.243 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:REDACTED -- port:143 -- socket:0x600012e11860 -- thread:0x600009fe3c00
8.614 NO [AUTHENTICATIONFAILED] Authentication failed.

WROTE Apr 22 08:02:03.244 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:REDACTED -- port:143 -- socket:0x600012e11860 -- thread:0x600009fe3c00
9.614 LOGOUT

I'm on Sequoia, but from the various threads on the apple support websites, it seems like the UI for this hasn't worked for coming up on a decade. It's the same if I add the account via the Internet Accounts setting in the System Settings app. So - how can I change the port used by a Mac Mail account? Is there a plist I can edit, or some command I can run from the terminal, to set the port that Mac Mail will use? To be completely clear, I'm not looking for any answers involving the broken Mac Mail or System Settings UI.