Comment 4 for bug 879305

I don't think "delete after 0 days" means "don't delete" : Actually it means delete immediately.
A normal user (one that is not a programmer and/or doesn't read launchpad bugs), may not even think about giving a zero value, even I wasn't sure if it would work (or instantly delete all the messages from my company's server)
I think there sould be a checkbox (at least visually, the checkbox can still store a 0 value internally)