'Compacting' (not compressing as that is like zipping) is a vital part of general maintenance and should be done either manually on a regular basis or automatically when it can recover a given amount of space. Info explaining what it does and why it is important: * http://kb.mozillazine.org/Thunderbird_:_Tips_:_Compacting_Folders I also do not like the pop up, so I choose to do compact folders manually at the end of each day, after I have deleted emails and emptied Junk and Trash. How to switch off the auto compacting and the pop up: Via 'Menu Bar': 'Tools' > Options' > 'Advanced' > 'Network & Disc Space' tab OR via 'Mail Toolbar': 'Menu icon' > 'Options' >'Options' > 'Advanced' > 'Network & Disc Space' tab Under 'Disc Space' '''uncheck ''''compact all folders when it will save over xx MB in total' click on 'OK'

Thank you, Toad-Hall, for the lesson ;-) /hans peter