Suricata

Add smtp_envelope and smtp_header keywords.

The envelope is composed of communication before the DATA segment ( example at http://en.wikipedia.org/wiki/SMTP#SMTP_transport_example) and the header is the part of the email content before there is the mail body (which should be anything between DATA and the first occurence of CR LF CR LF).

The idea is to allow rules searching for email addresses, mail user-agents, etc.. while not matching on the same pattern(s) being discussed in an email body.