Back in the day (I haven't run my own mail server for years and years) there was a company called Secondary MX.
That's all they did. They weren't a mail host or provider, there was no UI, nothing. All they did was allow you to specify them as, well, a secondary MX, so if you were offline they'd cache your inbound email until you were back. Simple. Efficient.
That's all they did. They weren't a mail host or provider, there was no UI, nothing. All they did was allow you to specify them as, well, a secondary MX, so if you were offline they'd cache your inbound email until you were back. Simple. Efficient.