> - provide integrity when sending the message by including a PGP signature. what's to stop someone from running an e-mail server and spamming mass e-mail lists

> - provide integrity when sending the message by including a PGP signature. what's to stop someone from running an e-mail server and spamming mass e-mail lists with message headers that spoof your mail domain, and proclaim bogus security lapses? This is a good point, but wouldn't use of SPF/DKIM solve this too? I think email servers are able to understand the SPF records and DKIM-Signature header and hence more accurately classify the emails as spam (if appropriate) which seems like a useful benefit.