Gregory Anders authored May 14, 2021 and Kevin J. McCarthy committed May 14, 2021

Add an option to convert the date used in the Date header into the local
(sender's) timezone. This is the current behavior and the option
defaults to true. Unsetting this option causes the date in the Date
header to be formatted using the GMT timezone.

This option is useful for privacy-sensitive users who may not wish to
divulge their sending timezone.