Rachel,
One of the things you might want to consider is compacting the 
mailboxes, which is a bit like running a defrag on your mailboxes. From 
the mailbox you want to compact, you'll find a "compact mailbox" option 
in the file menu; I usually use the keyboard shortcuts of alt-f, 
followed by the letter F. Try doing that first and see if the 
responsiveness improves.

Feel free to visit my Web site
http://www.davidgoldfield.info

                  David Goldfield,
         Assistive Technology Specialist

On 2/23/2015 5:26 PM, Rachel wrote:
> Hi, everyone.
> I'm using the latest version of Thunderbird and have noticed that over 
> time, it's taking longer and longer for the program to allow me to 
> reply to larger messages.  I'm thinking that the problem may be due to 
> the fact that my Sent and Saved mailboxes are quite large.  Since the 
> program seems to load all mailboxes at once, my thinking is that I 
> could move my current Sent mailbox to a different location on my 
> computer so as to preserve it, which I'd like to do, so that I could 
> start fresh with an empty Sent mailbox.
>
> In looking at my profile for, say, the Sent mailbox, I notice there 
> are three files that seem to relate directly to it: one called Sent, 
> one called sent.msf, and one called sent.mozmsgs. From what I can 
> tell, the .mozmsgs file is the one that contains the actual text of 
> the messages belonging to that mailbox.  But what are the other two 
> files?  And if I move my sent.mozmsgs to a different location on my 
> computer, should I also move the Sent file and the sent.msf, too?  And 
> if I move any of these files and restart Thunderbird, will it 
> automatically create a new, empty Sent mailbox?
> I hope my questions are clear and that I haven't completely confused 
> everyone.
> Thanks for any help any of you can provide.
> Rachel
>
>
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