Has your anti virus worked out Thunderbird version has changed?

I'm not running any antivirus software on my Mac

But interesting new wrinkle, I'm now also getting an error message at each startup that TBrid can't summarize the Sent box either, so now I'm unable to view any received or sent mail.

Also, when I startup Tbird with the internet connection disabled, the entire IMAP inbox is blank, empty, so everything that used to be stored locally for offline viewing is now not there. and all the attachments on my previously Sent mail are not viewable

One more interesting wrinkle is that all my email boxes on all accounts, yahoo, Godaddy, Office365, etc whether POP3 or IMAP are sorted in reverse order with oldest mail (ie: from 2012 or so) at the top then the recent sent or received mail at the bottom. Even tho I sort it and save it with most recent mail at the top, every time I shutdown and reopen, the software displays the oldest mail at the top.

I might have to stop using Tbird for mail to get any work done, and that would be a real shame, I really don't have time to find a new email software, and don't see how I can step backwards one or two versions to restore it back to humble working condition

Do you use anything like CCleaner ? If yes, then you need to stop CCleaner from accessing any thunderbird file or folder. It has a habit of clearing out all sorts of session and password files etc which are not helpful in thunderbird.

I'm on a Mac but not using CCleaner

okay another new interesting wrinkle - my IMAP inbox is only displaying the headers, not the body/content/text. Having to wait 5-10 minutes every hour for inbox to repeatedly rebuild itself just for me to read simple content.

Have taken to reading new mails on my iphone and ipad mail rather than my laptop because of these Thunderbird issues. please don't make me use apple Mail in my macbook, that software just absolutely stinks

What happens if you restart Thunderbird in Safe mode ? In Thunderbird Help > Restart with addons disabled

Report back on results.

Interesting results. and editing my earlier reply of 30 minutes ago

If I'm connected to the internet and restart in Safe Mode, then the IMAP inbox and sent box synchs and loads the email headers fine but not displaying the bodies of the email. Randomly does not display some emails content, no rhyme or reason that I can see.

My Mac was giving me an error message notification outside the software when I click on individual emails saying the inbox server wasn't responding, but of course now as I edit this post I can't duplicate the darn error notification, and it's not notifying me in the software window itself.

When I disconnect from the internet connection and restart TBird in Safe Mode then the IMAP inbox is completely blank, 8000 emails missing. That would seem to mean the copies of all previously synched emails aren't actually staying on my local drive for offline mode though I've had that option selected for a couple years. I need that for when Im flying without wifi, I often read emails on the plane in offline mode.

When I reconnect to the internet and restart Tbird again, then all the headers appear instantly, but it takes several minutes for the body content to re-load.

Not sure I'm wise enough to know what exactly that means, and also not sure I want to permanently disable add-ons that weren't a problem before v52.4.0, not even sure that indicates if they are now actually the problem?

okay great, another new update, now my IMAP inbox in Thunderbird is missing all old emails from 10/4/17 to 6/5/17. Why four months missing- I'll never know. It's re-building....again......

luckily all the email is on the webmail program and my iphone and ipad, but wow this is getting really frustrating with Thunderbird and IMAP

lets summarize.

You are using IMAP. This is synchronized to the server. No internet connection = no mails because there is no synchronization.

Is Thunderbird set to store copies of emails locally or only the mail list? Do you have free disk space for Thunderbird to work in? An error stating an inability to open a file usually means there is either contention from another program locking the file. On macs this is often some sort of backup. Those streaming backup are not as good as they are sold as being.

Otherwise it indicates that the file is corrupt.. This can be a first indication of a failing hard disk, or the result of corruption from other causes. However running some disk integrity checking software is indicated.

Mail missing from the list may just be some sort of server glitch, or a communications glitch.

Right click the folder and select properties and then repair. (yet another rebuild will ensue. Finally on preferences, clear the cache. This can cause weird things with IMAP especially if the body of the email is not stored locally.

Thanks Matt, I decided to edit my question to further clarify this all started 2 days ago when TBird automatically upgraded to v 52.4.0. Up until that point I had no problems with my work Outlook IMAP mail account synching or offline viewing, it all worked fine before the upgrade.

My Mac isn’t even a year old and no other software is acting up, so I don’t suspect a hard drive issue. In fact all my POP3 email accounts in TBird are working just fine except for my missing AddressBooks in a separate support thread . It all seems to point back to the moment the v52-4-0 upgrade plopped into place

Yes I had all the settings for offline viewing on previously without any issues. Old mail was viewable in the IMAP account whether connected to internet or offline. Other than the upgrade, I didn't change anything from last week to 2 days ago. Now, whether the software changed something on it's own or not I can't say.

Have done Properties>Repair on the inbox as suggested, and cleared the cache too. After that and a restart of Tbird in regular mode, the IMAP folder does rebuild and synch faster than earlier today, but it's still rebuilding a year's worth of inbox and sent mail in that account that it wasn't rebuilding before the software upgrade. Oh, and it's still rebuilding it on each restart with mail in decending date order instead of my preferred ascending order, can't seem to make that 'stick'.

When I tried an offline restart (after the repair and cache empty) disconnected from internet I was able to see the IMAP inbox but the IMAP sent box was empty. I got an error message: "Unable to open the summary file for Sent. Perhaps there was an error on disk, or the full path is too long." Ironic just like the inbox

Have initiated a Properties>Repair click of the Sent folder too, just to see if that snaps it out of it's misery. Seems like each "Repair" of each box might be helping a little bit, but that is a complicated step to keep taking on each restart.

Nope, just restarted several times after the Preferences>Repair on the Sent folder and it's still rebuilding. Faster yes, but still rebuilding.....

sigh

today's update: I went into Add-On's in TBird Tools this morning and manually disabled 3 of the 4 add-ons (but didn't remove any yet) while in regular mode.

Disabled: LookOut Lightning Exquilla for Exchange

Left enabled: Sort -Manual Sort folders

Repaired my Office365 work IMAP inbox and sent boxes one more time in Properties, and emptied the cache in Preferences one more time. Restarted in regular mode and everything is okay, not great, but okay and usable. No error messages on startup. Doesn't seem to be rebuilding the *entire* Office365 work IMAP inbox and Sent box from scratch, or it's doing it so fast at startup that I don't mind as much.

In offline mode, some of my Office365 work IMAP inbox previous mails randomly checked are fully readable while some are not; same with the IMAP sent mail in offline, some readable most not. at least Yet. Hopefully they will both re-build and re-propagate over time.

[ Collected Addresses Book is back to normal and full of it's contacts. Mac OSX Address Book still empty, but that's a separate support thread ]

Last night I tested Apple Mail app and Spark app and Airmail3 app just to see how they did with my Office365 work IMAP and one of my Yahoo accounts. No major problems but don't like their forced folder interfaces as much as TBird's comfortable simplicity. Will decide if I can live with Tbird in it's current mostly-repaired state or have to jump ship to a different 3rd party software or to <gasp> Apple Mail

> tested Apple Mail app and Spark app and Airmail3 app just to see how they did with my Office365 work IMAP and one of my Yahoo accounts.

So these are the two accounts? Yahoo is pop? (Yahoo has beeen known to have problems)

> [ Collected Addresses Book is back to normal and full of it's contacts. Mac OSX Address Book still empty, but that's a separate support thread ]

You didn't mention Collected Address Book earlier.

Your comment suggests Thunderbird hit a limit on open file descriptors

which happens to match your description in https://support.mozilla.org/en-US/questions/1179365#answer-1020693