I have used Thunderbird for years. A great e-mail client compared to the unnecessarily stuffed and often unclear use of web-based Gmail and commercially filled stuff from Microsoft.
But formatting the body is a complete disaster, especially after responding to an answer. I find the advice to consult the Help files unnecessary here. Incomprehensible that so many continue to accept that.
eM is a revelation, very good, the entire body can be formatted independently of answers.
I am a happy chappy now.
Perfect email client !!