Sender's Last name, First name. "Subject line of email." Received by (name of receiver), Date of email.
Abbott, Emily. "Re: How to format an annotated bibliography." Received by Marilyn Brown, 21 Nov. 2016.
Citation format according to Purdue OWL (Online Writing Lab):
Editor, screen name, author, or compiler name (if available). “Posting Title.” Name of Site, Version number (if available), Name of institution/organization affiliated with the site (sponsor or publisher), URL without http:// or https://. Date of access.
“SWC Teachers Suspended after Rally Participation.” Save Our Southwestern College, 23 Oct. 2009, 7:30 a.m., saveourswc.blogspot.com/2009/10/swc-teachers-suspended-after-rally.html. Accessed 17 Nov. 2009.
Cite as a short work from a Web site. Use the text of the post as the title in quotations; if no title, label it as Post.
"I Thought the Truth Would Be Enough." Only Human, from NPR, June 28 2016, www.npr.org/podcasts/449020426/only-human.
@Steven_Hawking. "Run, jump, throw: The physics behind Olympic events explained." Twitter, 12 Aug. 2016, 5:30 a.m., twitter.com/Steven_Hawking/status/764076653727260672?lang=en.
For more examples, please refer to MLA Style Center.