Like most people i have a number of email accounts setup in Thunderbird. Whats
really needed is a simple setting like a checkbox on the Account Settings page
that would suspend completely all sending and receiving for the account without
losing the password, emails or other important data.
this should prevent the account from doing any internet activity like
contacting the server EVEN if the "Get all Messages" menu-button is used. In
all cases it should just skip over that account if the checkbox is checked to
disable it. Unchecking the box would resume normal behavior with no further
input required of the user. e.g don't come back and ask  for the password again
because like with a lot of people its long forgotten
I have a bit wordy because googling around there are all sorts of wacky
suggestions like inserting a space in the user login name or deleting the
password, none of which are acceptable, nor do they work properly.