Mail won't open. An error occurred during the import

The mail program works. I am unable to sign into any of my email accounts. I thought it might be that I have reset passwords on one but certainly not all I tried, so I suspect the login issue is really the outgoing server issue that needs some goofy password that is in my email. I'm not resetting all my email passwords. All the accounts were working before this crash.

Now that the program works, how do I reopen and rebuild my email database?

Rebuild mailbox requires being in Mail, which still doesn't work. Reindex messages was the option I chose. It fired its st started with back up everything. My time machine exceeded its hard drive capacity, so I had to start over with a new time machine on a new hard drive. It took two days to get that process done.

I followed the instructions though I am in V4 because that is where Sierra puts the emails. On the positive side, it does identify which boxes it is rebuilding and I saw the older, most critical email boxes successfully processed (I assume because it moved on to others). Curiously, my apple ID email, which has virtually no other traffic, is huge--took a long time to process. Strange for an unused email address. Immediately after that address, it collapsed as usual telling me only to quit, no other options.

While I am here in the V4 folder, there are a few dozen folders with titles like "A43B62CD-1510-4FAA-AAAB-BF80D9352B70" That particular one is over 17 Gb, over 11 Gb is in the Junk.mbox folder Only two other similar folders are over 1 Gb and none that huge. Opening one of the emails in that folder in text edit, I can see the email address is my apple ID email

I don't know how this email database stores stuff. Is it safe to delete that 11 Gb Junk box? Or does all this have to cross reference?

Also, I have IMAP folder for that address and one other email. I don't recall using IMAP successfully for any of my boxes. All POP. Essentially I am looking for places I can safely delete unnecessary crap to reduce the amount of stuff to be processed and potentially stuff causing problems.

I talked with a Genius. I essentially deleted the Apple ID email account contents, reducing my number of emails from 1.6 Million to a little over 100 thousand. I arrived at this incrementally. That finally did the trick. I am dealing with my hosting company for that account. It is apparently just serving that content back to me after I delete it.

The big question is who did Apple sell my information to? They are the only people who know

this problem address.

I have 20 different email addresses due to my responsibilities with numerous different entities. The email address used for my Apple ID was created for a now dormant entity 15 years ago. Apple is the only place that email address is used. If Apple didn't sell it, and nobody else knows it exists, how did that turn into serial SPAM?

What I only discovered a few weeks ago, is for every email I delete or identify as junk, much less the ones that automatically go to junk, it is immediately replaced 5 minutes later in the next email sync cycle. My junk mail never showed a number over a few thousand, but they obviously were there corrupting the system.

As far as that email address, I am deleting it entirely through my hosting service. I am creating another unique email on another domain, just for the Apple ID.