Alin Iorga wrote:
> Hi,
>
> I am using Thunderbird 1.5.0.9 (20061207) on a Windows XP and it
> seems that a memory leak was introduced in one of the latest updates
> (I have been using Thunderbird for some time and it did not created
> any problems until recently).
>
> On my profile I am accessing several email address both POP3 and
> IMAP. It seems that only for one of the email addresses when it
> downloads emails from server the memory usage of the application
> increases a lot with every downloaded message (for downloading around
> 100 small messages it uses several hundreds megabytes of RAM). This
> issue happens just for one email address (same address every time).
>
> I hope this is the correct address to report such a problem and
> please help me find the cause for it. Please tell me you need
> additional information.
>
> Thanks, Alin.

Try two things :
Select mail account name in folder pane , goto File > Compact folders
Do same for other mail accounts.

if still getting same problem :
*completely* close TB
goto TB profile folder ("http://kb.mozillazine.org/Profile#Thunderbird")
open Mail folder
delete all .msf files
Start TB