Mail for his.com and a number of other domains is currently down and the problem has been identified. Incoming mail is queuing on backup servers and will be delivered when the problem is resolved. We’ll post updates here.
Update 12:30 pm 9/18/21: this problem has been resolved. No mail has been lost – incoming mail during the outage is queued on a backup server and will be delivered over the next 60 minutes.
Update 2:30 PM 9/18/21: queued mail for accounts affected by this outage has been delivered and operation has returned to normal.