lammert - 1:24 am on Jul 12, 2010 (gmt 0)

I use -all on some domains, but not on all. The problem is that you don't always know which server will send legitimate emails with your email address as source address.

A number of online systems like forums, webshops, mailinglists etc send notification emails where the address you used to sign up is used as the From: address. Those emails may get lost if you use the -all setting because they are sent from servers whose IP address is not in your SPF record. If you are never using a domain to sign up to sites which send messages on your behalf, it is safe to use -all in the SPF record of that domain.