I’m not here to recommend a NUC (because I don’t know), but a thing about the Pis: I have several, some have been constantly running in some form ore another for 10 years, and I have had 0 issues with overheating or SD-cards. Also I only use the official power supplies.
The Pi 4 and 5 have heating issues, so I added passive cooling to them (if I would do heavy tasks like transcoding I would add active cooling, but that is not my scenario).
They are reliable little machines :-)
(Also they are limited in CPU and memory, so I also have a NUC. It’s an official Intel so not the kind you want ;-) )
As other people said, getting the mail delivered is the hard part. Check if your mail is received by Google, Microsoft, because apparently they blacklist by default.
You can do everything yourself and then set up a relay for sending, so all mail is sent through someone else who can make sure it is delivered. Then you could get something like purelymail, which is 10$/year to deliver your mail. (I have no relation with purelymail, I am their customer, but it took me quite a while to find a mail relay that is not for sending bulk spam but for real people).