Changed 'Date' format from RFC822 to RFC822Z
Changed 'Date' format from RFC822 to RFC822Z

Some email clients including Microsoft Outlook on OSX treat
the 'Date' field when formatted as RFC822 as +0000, and so add on the
local time zone off-set. For users infront of GMT, this causes emails to
appear to be recieved in the future. For example, an email sent at 12pm
AEST on 2017-07-20, will display in Outlook on OSX as being recieved
at 10:00pm 2017-07-20.

Swapping the date format from RFC822 to RFC822Z (which includes the time
zone) produces the expected behaviour in Outlook on OSX, Outlook on
Windows, Gmail and Mac Mail.

scorredoira/email