I have an Archive location set up through my network on my NAS. One of the disks failed and the NAS was turned off until the faulty disk could be replaced. When I then tried to open Thunderbird it stalled, presumably because it couldn't find the archive location. Once the disk had been replaced and the NAS powered up, Thunderbird opened straightforwardly as expected.

Would it not be better to open Thunderbird with a suitable timeout, without the NAS connection, but provide a pop-up to advise that "the archive location has not been found - you are unable to archive at this time". That would allow emails to be read and sent in the usual way and also warn users of other issues that would affect archiving. Any archiving could be left until the connection to the archive location is restored.