[MlMt] Import message archive (.mbox file) not connected to an IMAP account in MailMate

[Topher Buck]

I subscribed to Hey (https://www.hey.com/) for a year, as an 
experiment, but have decided to stick with MailMate + Fastmail and not 
renew my Hey subscription. I exported my Hey messages as a mail archive 
(.mbox file). The only export option Hey offers creates a single .mbox 
file, and I’m having trouble importing it into MailMate. I’m not 
sure why. When I try, MailMate pulls in approximately three weeks’ 
worth of messages (178 messages, to be precise), then stops. MailMate 
doesn’t hang or freeze entirely (I was able to compose this message, 
for example, though I could not send it until I’d restarted MailMate), 
but if I quit MailMate, the open window(s) close, but the program 
doesn’t fully quit; I have to use Force Quit.

Do any of you have any suggestions? I made a copy of the .mbox file and 
opened it with a text editor to confirm that it contains more than 178 
messages; it appears to be complete. Is there a way to import the 
message archive into MailMate without trying to connect them with an 
existing IMAP account (that is, connected with no IMAP account)?

Thank you,

/topher