The hardware looks slick, but are my emails going to bounce when my not commercial comcast/spectrum/at&t/whoever has a maintenance outage? I'm not sure it's too useful to bring that out of the datacenter and into my house...
If you are unreachable, the mail server that is trying to contact you should try again later.
How many times, at what interval and for how long retries happen vary.
Most servers will notify the sender saying that “message delivery failed permanently” if the receiver is unreachable for such a long period of time that the sender server gives up.
So between the resilience to temporary unreachability and the fact that the sender should be notified if delivery times out, I would say that the chance that anything important is lost is very slim.
The bigger problem is the fact that home ISPs often block outbound SMTP, as well as the fact that their IP blocks are often regarded as low trust by others, meaning that you will certainly run into problems sending mail every now and then. I did not yet read the OP link, but am going to, so I don’t know if they offer proxying/forwarding of outbound SMTP.
The problem is that the major email hosts send to the spam folder any emails from IP addresses they don't explicitly trust.
My solution to this is just to ignore it and tell people if they want to receive my email they should work out how, as the problem is on their end not mine.
But lots of your customers won't like that answer.
> In a typical system, the program that composes a message has some method for requesting immediate attention for a new piece of outgoing mail, while mail that cannot be transmitted immediately MUST be queued and periodically retried by the sender.
[ ... ]
> Retries continue until the message is transmitted or the sender gives up; the give-up time generally needs to be at least 4-5 days.