Some places observe daylight saving time/summer time during the summer, and therefore use MDT (Mountain Daylight Time) in the summer. Email Time Zone Indicator: -0700. An email sent from someone in the Mountain Standard Time (MST) time zone will have the time zone listed as -0700 in the headers of the email. (However, -0700 does not have to be in Mountain Standard Time, as other time zones could have the same UTC offset).