I hate Thunderbird. There are so many things that suck. But I haven't found anything better.
I use it on my Fedora linux system (currently Fedora 32).
First find the hiddent Config editor. Go to Edit -- Settings -- General and scroll down to the very bottom and look for it on the right.
Find "mailnews.wraplength" and change the default value of 72 to 0. The interface to change values is also brain-damaged, but with some trial and error you can set a value of 0.
As of 8-2020 I downgraded from Thunderbird 68 to Thunderbird 60 in order to retain support for the Keyconfig add-on, which I consider essential.
At some point keeping an old Thunderbird became unwieldy and I "just gave up".
As of 6-2024 I am running Thunderbird 115.0.0 -- who knows why the version number keeps changing, I never see any changes or improvements, rather they change things that break stuff (like the keyconfig add-on).
I am revisiting this in 1-2024 after doing a full install of Fedora 39. This caused me to also install Thunderbird from scratch, and I lost whatever configuration I had done in the past to make this work. Thunderbird seems to take the view that "you will only use the Firefox browser". Very likely all of this would "just work" if you used firefox.
When I tell Thunderbird to use my default browser, it simply does nothing (does not work). Just how it determines the default browser is unknown to me, but in my case it is google-chrome (at this time anyway). I finally rolled up my sleeves and dug into all this:
Back in 2021 I had to deal with a similar issue. Back then I had reverted to an old version of thunderbird that allowed me to use a nice keyboard shortcut mapping addon (which I used to turn them all off). Newer versions of thunderbird broke that addon, and they provided no builtin feature to manage keyboard shortcuts (as they should). It eventually became more of a problem to deal with issues in the old thunderbird I had locked myself onto, so I waved goodbye to the keyboard add on and went back to using the latest thunerbird. You can read about all that in the following notes.:In 8-2021 another issue reared its ugly head, namely it has become difficult or impossible to specify the browser Thunderbird launches for html links in emails (it defaults to Firefox). To fix this I had to go with the latest thundergird and stop downgrading to an old version.
I tried various web based email readers, but they are all miserable compared to Thunderbird. Their only virtue is that you can use them from any device with a browser. My usual "other device" is a cell phone or android tablet, and there are android specific mail apps that work nicely there.
I have looked at other linux hosted mail clients, but was never satified. I should look again.
Here are links to specific topics I have found to be important:
Mail is received from imap.gmail.com via port 993. I use SSL/TLS on the connection and authenticate via a normal password.
Outgoing mail goes to port 587 on smtp.gmail.com. I use a normal password to authenticate, and connection security is via STARTTLS. Thunderbird particularly annoys me by binding the "Delete" key to the "delete this email action, this has burned me badly several times.
The first thing to do is to find your "profile", which is in the ~/.thunderbird in your home directory (or the backup copy thereof). In my case, the items of interest are:
./3pva2om0.default: -rw-rw-r--. 1 tom tom 6924 Feb 13 22:47 abook.mab -rw-rw-r--. 1 tom tom 21300 Feb 14 11:10 history.mabI copied both of these files to the same location in the new profile and that seemed to do the trick.