date
    Local
date -u
    UTC
date -R  (aka RFC 2822)
        Local time +-ZONE-OFFSET
    where, rather counter-intuitively, the shown ZONE-OFFSET
    has _already been applied_.  To get UTC, you have to subtract the given
    offset from the displayed local time.  E.g. if you see
        X - Y
    then the UTC is X + Y.

Times in emails are often in long date -R format.