Thunderbird e-mail client: Why is it failing to download so many e-mails?

Factual Questions
1

I’ve been using Thunderbird for my e-mail for a couple months now, and I’m encountering a strange problem: It doesn’t download everything.

A while back, I sent an e-mail to my pastor’s wife. I didn’t receive a reply for a very long time. But, I happened to log into my e-mail account via a webmail interface, for reasons I don’t remember now, and there was her month-old reply. For some reason, Thunderbird failed to download it.

Today, I logged into the webmail version of my inbox, and holy crap, there were over 1,200 e-mails that Thunderbird has not downloaded! Granted, the bulk of it was spam, but amongst the clutter I found several e-mails addressed to one of my e-mail discussion lists. All of the “original posts” showed up in my Thunderbird client, but all of the replies were left on my mail server, un-downloaded. I’ve so far (still working my way through it) found several other legit e-mails that have remained unretrieved.

WTF is going on here?

ETA: I have my own domain name, with its own associated mail server. My previous e-mail client, which I used for more than 15 years, always downloaded everything, but, sadly, I had to replace it because it hasn’t been updated in forever and was constantly glitching on me after I upgraded to the latest version of Mac OS X.

2

Running your own mail server can be a huge PITA. Have you checked your mail logs, both in Thunderbird and on your server? If you can trace it by subject or sender or message ID all the way from initial receipt, past the spam filters, past Thunderbird’s own filters, etc… that’s the only way to find out for sure what happened.

Or just add Google Apps for Work to your domain for $5/month and you can use Gmail instead of Thunderbird. Nothing against Thunderbird, but Gmail is phenomenally good at just making your email work once you hand over your MX to Google.

3

Probably been a decade since I’ve debugged mail client activity, but I’d recommend some quality time with your favourite telnet client. I presume you’re downloading via POP - find a list of text commands and see if what you’re expecting to see actually jives with what the POP interface reports.

For example, LIST should show how many messages are pending, with a summary of each - if your message is in there, then you’ll know the client is ignoring it. If it isn’t, then the server thinks the client acknowledged it.

My bet is one some weirdness with the message IDs, but you’ll have to check for yourself.