In the message view the "Date:" header is always shown in user's local timezone, with no reference to sender's original one, so the only possible way to find out the original time is to manually inspect the raw message, and look at the Date: header.
It would be useful to give the user the choice to choose whether to display the message date in his own or in the sender's timezone, maybe keeping the local timezone in the message list and the original one in the headers view, so to facilitate the message sorting while avoiding the need to manually inspect the message.

Example (my timezone is UTC+2):
(header)        Date: Thu, 27 Apr 2017 14:19:49 -0400 
(message view)  27/04/17 20:19
(message list)  giovedì 20:19