Email messages sent to you in a personal email or one posted in a newsgroup is considered non-retrievable or unpublished. If you choose to use information from email messages you can cite them respectful of privacy issues but include the year and the professional affiliation of the author.
Author. Affiliation, City, State. Personal communication, Year.
Gaynor, K. Thompson Rivers University, Kamloops, BC. Personal communciation, 2011.