Mozilla opens normally and new emails are listed normally. I can read them normally. However, if try to delete mail I get "Program not responding" same if I try to move mail to another folder. or even if I try to close it.

It will perform all the above functions but it takes 10-15 seconds to do it with every other commend apart from opening mail and reading it? Some companies are asking for my correct address which indicates that not all my incoming mail gets through.