This article is from the PGP FAQ, by Jeff Licquia firstname.lastname@example.org with numerous contributions by others.
> Some BBS sysops may not permit you to place encrypted mail or files on
their boards. Just because they have PGP in their file area, that
doesn't necessarily mean they tolerate you uploading encrypted mail or
files - so *do* check first.
> Fido net mail is even more sensitive. You should only send encrypted net
mail after checking that:
a) Your sysop permits it.
b) Your recipient's sysop permits it.
c) The mail is routed through nodes whose sysops also permit it.
> Get your public key signed by as many individuals as possible. It
increases the chances of another person finding a path of trust from
himself to you.
> Don't sign someone's key just because someone else that you know has
signed it. Confirm the identity of the individual yourself. Remember,
you are putting your reputation on the line when you sign a key.