Email already supports delivery to destinations which are intermittently connected. The legacy MTA behavior is to retry automatically every few hours for sever

Email already supports delivery to destinations which are intermittently connected. The legacy MTA behavior is to retry automatically every few hours for several days, with failure resulting in a notification to the sender. Operators have adjusted the behavior over the years to support grey-listing so the retry period and interval are both shorter -- but still in use! While communication between two hosts which are rarely simultaneously connected is best facilitated by a third party, some tweaks to your MTA's the delivery retry interval and period could enable reliable communications between email users who are connected simultaneously on a regular basis.