Auto-Purge
 

I observe that auto-purge is present for some folders but not for others. Do I have any control over which folders have auto-purge (of any length) and which do not??

Yes, go into folders, choose a folder, then edit, click on show advanced preferences - there's the option to autopurge.

For example, I have a folder called "7-days" which is for newsletters and such, and as indicated, the folder autopurges in 7 days:

http://emd.fastmail.com.user.fm/test/autopurge.png

All that option does -- assuming we are on the same page here -- is allow me to adjust the length of the autopurge period. Suppose I wanted to turn it off altogether? What do I do then?

Hmm, that's a difficult one, I'll take a wild guess.

Uncheck the autopurge box?