Format: 

Lastname, Firstname of sender. "Title of Message." Received by Firstname Lastname. Day Month Year.

Lastname, Firstname of interviewee. Type of interview (e.g. Personal interview, Telephone interview). By Firstname Lastname of interviewer, Day Month Year.

Examples: 

Jones, James. Personal interview. By Sandra Smith, 31 Jan. 2012.

In-text: (Jones)

Doe, Jane. "Re: MLA Citation Guide." Received by James Jones, 14 Nov. 2010.

In-text: (Doe)

Notes: 

For personal and telephone interviews including the name of the person who conducted the interview is encouraged, but optional (https://style.mla.org/personal-interview-on-two-days). For email correspondence, you should provide the title of the message as it appears in the Subject line of the email (MLA 29). If no subject was given, you can provide a brief description of the message, but do not enclose the description in quotes (e.g. Email about overdue book) (MLA 29).

Source:
MLA - p. 29