[Users] 'Invalid Credentials' Error

[Dustin Miller]

Basic Context: Claws Mail v4.3.0git44 on Linux systems, with frequent
syncing from one machine to another and back again using (g)rsync to
ensure data integrity. Using POP3 and Oauth2 for affected accounts.

Every so often I run into an issue where one or more of my three Gmail
accounts gives an 'Invalid Credentials' (fatal) error when I try to
download mail. (From my memory, in the past it has only been one
account, but today it was all three.)

Workaround: I somehow managed to figure out that in order to solve this
problem and get things working again, all I have to do (for each
affected account) is use the menu to go to Configuration - Edit
Accounts, then select the account, click on 'Edit', then click on 'OK'
to close the 'Edit' window, and 'Close' to close the 'Edit accounts'
window. (And just to be clear, there is no need to make any changes to
any of the account settings. Also, I didn't check whether clicking on
'Cancel' instead of 'OK' in the 'Edit' window would have the same
effect or not.)

I'm not sure how to understand this, but it seems like strange /
unexpected behavior. However, I don't know what causes the initial
problem and so have no idea how to try to reproduce it, so don't really
have enough info to file a bug. My best guess is that, on rare
occasions, there is some sort of disconnect happening within the Claws
Mail system and then somehow the opening of the 'Edit' window for an
account and/or the clicking of the 'OK' button in that window 'fixes'
that disconnect.

By the way, I did also try 'resetting' (i.e. on/off) the network
connection on my machine, and also tried doing a restart of Claws Mail,
but neither of those had any effect. Luckily, I remembered about it
happening once or twice before in the past, and had a vague memory of
how I 'fixed' it then.

Anyway, just thought I'd post this info here in case there are:

* 1. Developers who might have a better idea of what's going on and
  if/how a 'fix' for this 'bug' could be implemented in order to
  prevent this from happening. (If anyone in this group is wanting to
  pursue this, I would likely be able to help out with testing. Or if
  you let me know what information would be helpful for me to collect
  if the problem happens again -- maybe some sort of a before and after
  comparison of one or more files in the config directory, or something
  similar?)

* 2. Other users who have faced this problem but have not figured out a
  workaround.

Cheers,
Dustin