Convert date_time to IMAP4 INTERNALDATE representation.
Return string in form: '"DD-Mmm-YYYY HH:MM:SS +HHMM"'. The
date_time argument can be a number (int or float) representing
seconds since epoch (as returned by time.time()), a 9-tuple
representing local time, an instance of time.struct_time (as
returned by time.localtime()), an aware datetime instance or a
double-quoted string. In the last case, it is assumed to already
be in the correct format.