Over time Mozilla’s Thunderbird may happen to require some maintenance in order to continue running smoothly. Symptoms could be that either you cannot find mails that are supposed to be there, mails are doubling without any reason, or deleted mails show up again in its original folder.
Note that Thunderbird must be closed (and really not running) for the next steps to be successful. You then need to navigate to your profile folder and execute the given commands at the root of this directory.
I really do not know why I did not check out Drush earlier. It is a command-line interface to comfortably maintain your Drupal-based website. Labeled by its creators as “veritable Swiss Army knife” it can virtually do any administrative tasks that you can think of. And this within a fraction of the time that you would usually spend to execute each single step via the original user interface of Drupal.
As prerequisite you should have a well setup Drupal installation. If not for example updating Drupal’s core might not work out well and even screw up your site. After installing Drush you can easily verify this by running the command drush core-requirements.
The current stable release of Drush is 8.1.12 and requires PHP 5.4.5 or later. It supports Drupal 6.X, 7.X, and 8.X.
The installation is straight forward and explained well in the official documentation.
The most annoying task for myself was always having to manually update Drupal core, especially when there are urgent security updates.
With Drush it is as easy as that (original description):
drush vset --exact maintenance_mode 1 && drush cache-clear all && drush pm-update && drush vset --exact maintenance_mode 0 && drush cache-clear all