Since its last major release, the mail program Thunderbird comes bundled with the calendar and task add-on Lightning. Which I ignored at first, then recently disabled. Then I noticed that Thunderbird didn’t check for new mails from my accounts (all POP3) every X minutes, even though nothing was changed in those options. A manual check for new mails worked fine.

At first, I didn’t connect this to disabling Lightning, but apparently that was the cause since after reactivating it, the periodic mail download works again.

I couldn’t find a hint about this connection on the net, so maybe this post helps someone now who encounters the same problem…

Update: After Windows hibernation over night, it again won’t work. Grmbl. What could that be…? At least after a Thunderbird restart, it works anyway (which didn’t help with Lightning disabled)…

Update 5.10.: Version 38.3.0 is said to fix the hibernation issue. Let’s hope that’s true.