Funny, my self hosted email has a better uptime than this pos
Email is actually designed with intermittent connectivity in mind. The sending server buffers outgoing emails until they're accepted by the receiving server. Typical settings are to retry every 4 hours, with a permanent failure being counted after 3-7 days.
Work's outbound email server for server/API/website emails (like password reset requests) has 127 emails in the queue, all to MS365 users.
Some of the big mail senders must currently have enormous queues of delayed messages.
It'll be partitioned by receiving domain. The server will rotate through each domain that has queued messages and try to deliver the first message in the queue. If it can't reach the server it'll move on to the next queue. Or something like that but not necessarily exactly that.