Can I somehow use gvim to compose my email messages in Thunderbird?
At this web site you can find a non official thunderbird extension to use an external editor of your choice:
As enzotib stated, you should use the external editor plugin.
The direct link to the plugin should be this: http://globs.org/file/exteditor_v090.xpi
You'll need to download the plugin, then go to Thunderbird and do: Tools -> Add-ons -> Install Add-on from file (from drop-down at top-right)
Then, you will need to set the preferences for the plugin so the external editor is gVim. On linux, that will probably just be 'gvim -f'.
Most importantly, you will then need to add the 'External Editor' button to your toolbar. Without adding the toolbar button the plugin would not work for me. Below I included a picture where you can see the 'External Editor' button that I'm referring to. After adding the toolbar button, you can launch the external editor with the toolbar button or CTRL-E
Try Teledactyl. You can do much more vim-oriented things with it but if you're only interested in editing files in vim, it also works, just disable all of it and keep the external editor feature on.
This is what I had (use GMail interface now) in my
:set editor='gvim -S .vimrcforvimperator -f'
I think you should use this tutorial to solve your problem.