First, when I refer to "New messages on the server", I am referring to new messages I can see on the ISP's webmail page. I realize this is not 'the server', but if I can see new messages on the webmail page I assume these messages exist as new messages on the server.
I have the last version of TB. I have tried (on different machines) a couple older versions of TB all the way back to 38.5 and have seen the same symptoms in all. My original ISP was Time Warner Cable, which of course does not exist anymore, but the accounts have all been taken over (in this area) by 'Spectrum'. With an @wi.rr.com email address, the only active Spectrum email server I can log into is still mail.twc.com. When setting up TB, it wants to auto-configure to
This issue surfaced when I bought this new Windows 10 machine to replace my -expiring- Windows 7 machine. So new machine, new copy of TB. I had been using POP3 on the Win7 machine, and had not had any problems. Set up the new machine for IMAP and have had the issue since. (I have disabled TB/POP3 on the Win7 machine, so it is not messing with the new messages)
Current troubleshooting:
I have created the logging .bat file (imap.bat) in my profile folder. I disabled all accounts in TB except my primary email account (one of the rr.com accounts). Last night, I made sure I had read all the new messages as seen on the webmail page, (so there were no existing new messages) and started TB via the .bat. The .log file appeared of zero size.
This morning, there are 10 new messages showing on the webmail page. TB has pulled 9 of them (this is good, usually it leaves more new messages on the server). Log file now shows a size of 850 KB.
What is my next step to get the log analyzed?
Update: There are now 16 new messages shown on the webmail page, but Thunderbird only lists 12. The imap.log file has climbed to 3724 KB.