Thunderbird is quite similar to Gmail, in many aspects, especially graphically. Both do the same job in a good way. I can tell that we use Thunderbird for years already, and in general we are pretty satisfied, so there is no reason to change software to try or evaluate …
We choose Thunderbird since it proved to be sufficient for our needs and is freeware. The choice was also influenced by a contact who is a certified cybercrime investigator
For the use we need, I can tell that Thunderbird works pretty well, even if we don't have a specific scenario to use it. We must simply manage our email in both directions, and Thunderbird is an easy and fast solution. For our experience it's a good software, not particularly customizable, but simple to use.
Easy to navigate threading and search capability seems limited
Very slow and clunky. I am still combing through about 10,000 emails that I'm slowly trying to delete (mostly junk/spam/transactional emails) and if I highlight even just like 20 emails at a time it takes about 5 seconds to delete them so no way to do this efficiently
Thunderbird is a software very simple to use, but efficient in every aspect. We don't have a specific need, apart to manage email in both directions, and Thunderbird does it's job in the best way. I would like to see a more friendly interface, with some colours more, to help the sight in the email searching. When we have many of them, sometimes it's difficult to find the one that we need.