(In reply to pantagana23 from comment #40)
(In reply to Jorg K (GMT+1) from comment #39)
Yes, "Tools > Account Settings" opens the account manager. In the panel on the left, you have a list of accounts with the default account underlined.
Found it, problem with no automatic download at startup solved. It seems that in 68.x version, default account gets unchecked.
For anyone having the same issue (one POP account, no extensions):
Go to Tools->Account Settings
This opens a window, which, in this thread, is called Account Manager.
In Account Manager you can see your mail accounts in left section, which are in bold font.
So if your mail account looks like i.e. Mail account 1, it is not default.
It should be in bold font, and underlined also.
You click on your email account, and then on bottom left part of Account Settings window you click a drop-down menu icon Account Actions.
When this opens, among other options, you will see option Set as Default, and click on it.
Now your Mail account 1 should also be underlined (don't know how to put underline on text here, but you get the picture).
You then click OK on Account Settings window, which should save changes.
Restart Thunderbird and that's it.
If the Set as Default is in grey, and not black font (not available option), you either didn't click on your account name previously, or your problem lies somewhere else.
Hope I helped someone.
This also made mine start working.
I have the folder sort add on and have had it for some time. Yesterday, I had the bright idea of changing my mail folder setup a bit by changing all accounts to use "Local Folders" as the inbox and everything else. I had my 7 or 8 email accounts all using a main accounts folders for a very long time and it always bugged me that I had that folder tree and "local folders" folder tree with seemingly duplicate folders in them like Junk, Trash, etc.
So I changed all accounts to use Local Folders for the inbox and all other folders, was a bit of a time consuming task to go through them all and select. Then I moved my emails from my primary sent and inbox to the local folders sent and inbox, closed TB and restarted it. Then my primary email folder structure went away and I now had a single folder tree.
Then I noticed it wasn't going to the "inbox" when I opened TB. So I tinkered with the setting in the "Manually sort folders" setup and got it to start landing on Inbox when I opened.
That's when I noticed my emails weren't downloading when I opened TB... I did what another mentioned to go through each account and verify that I had the box checked to download on start, which looked ok, so I checked/unchecked all and restarted TB. No luck. For fear that I was going to have to undo everything and go back to the 2 tree structure I had before, I ran across this comment. Sure enough, none of my email accounts were "default" anymore. So I picked the account that used to be the primary folder tree and set it as default. Now it's downloading mail again from all accounts on start and continuing to download mail from all accounts while it's opened.