You are trying to fix a splinter with a felling axe is my feeling here. Your have your issues with Thunderbird, but your description of them reads like a litany of the potential problems uncontrolled antivirus programs can cause in a mail client. I would almost say you have Norton as an antivirus as is has seen more mileage in this forum over the years for duplicate messages that the others of the same ilk. This is with POP mail account where the original messages are left on the server. Norton is a standout is in a field full of over achievers. BTW in this instance the antivirus crashes when it encounters a malformed email and takes the entire connection with it. Later Thunderbird tries again on it's timed fetch and again the antivirus will crash everything at exactly the same point. Until you either remove the malformed mail from the server (usually emptying the spam folder server side does the job) or you turn of the antivirus mail scanner until the malformed email is successfully downloaded (and guess what you are not infected with anything). I am particularly odd, in that I specifically do not believe in email scanning incoming or outgoing. I do suggest care when opening and saving attachments to email but I think the actually scanning is more trouble than it is worth. Note also that with POP mail account the record of what has been downloaded is stored in your profile in a file called popstate.dat and if you have an antivirus program scanning in the Thunderbird profile folder whi9le it is running contention can see the file data corrupted or invalidated so you get everything you have left on the server over again. Other cause the issue by placing the profile folder in their documents folder or otherwise cause the file system to be unstable with streaming backups, profiles on NAS devices or cloud backup of the profile contents in some form of home made synchronization between computers. Now as for getting lost when accessing the address book. Why would you leave the compose window to find an address? You basically lost me at that point. Press F9 to have the address books listed in the compose window if the automatic search when you type into the address field is inadequate. You are not using a phone and modern wide screen monitors are far to wide to fill with text anyway, so having your contacts in a pane on the right makes sense. At least to me, and I have it turned on at all times. But F9 does toggle the pane on and off so you are not stuck with it either way. Re your idea that Gmail allows you to retract email, great idea hey. I wrote about that in October 2011 and the same thing offered by exchange server implementations (including hotmail). See https://thunderbirdtweaks.blogspot.com/search?q=recall+an+email it is not really a recall as I discuss in the article, because Google have not actually done anything with the email. The sendlater addon I mention is also still available.