Hi fawkes!
I have found a issue when trying send mail using .onion and needed do some extra configurations on Thunderbird ( I have done a search on forum but not find).
These are the 2 simple steps to add on AnonGuide (I think should). On Thunderbird Go To:
→ Preferences - Advanced - General - Config Editor - Search to “network.dns.blockDotOnion” set TRUE
→ Preferences - Advanced - Network & Disk Space - Connection Setting - CheckBox ON “Proxy DNS when using SOCKS v5”
Thank you to Daniel!!! About this TIP!!!