I am reading about the access\_db feature of sendmail. Apparently it looks promising as a preventive way to stop spamming. 

I have several questions related to how access\_db is used. So basically I specify a set of rules in the access file, and sendmail will check this database to see if it should do anything about an email. 

1. How about the mails that do not fit any of the specify rules? What's the default behavior?
2. Can I use regular expression? For example, will "To:\*@spam.com REJECT" work?
3. If I only have "paypal.com RELAY", does it mean my sendmail will accept and send emails originated from or destined to paypal.com?

Thanks a lot!