Always used Thunderbird until today. I had to delete all my messages in Gmail as account storage was full so made sure I downloaded all messages to Thunderbird first to make sure I had an offline copy.

Unbelievably when I next started Thunderbird it deleted all the messages that I had deleted on Gmail even though it shouldnt have! I will NEVER use this application that I once donated money to but now hate with a passion ever again! I have now lost years of super important emails that I can NEVER get back!