I am in the process to switching from Thunderbird. One of the plug-ins available for Thunderbird was very useful;
I use my gmail from both work and personal, and thus have several email addresses that forward into gmail and automatically sort into appropriate folders.
The plugin, called “folder account”, automatically sets your identity, depending on what folder you are in when you hit “new mail”, or what email you are responding to.
This is a great feature, because when you respond to a work email - it comes from your work email address - for instance.
Here’s a link to the plug in;