Specifically email is not difficult to host because of the technical burdens but because of the black and whitelisting of the big players. Often your server IP address happens to be put on a black list without your fault and then you can write an email to Microsoft or Google and say ‘pretty please remove my IP address from your blacklist’ and they just don’t answer because they’re swamped with requests like that and they need to check each one manually or something and then suddenly you can’t email to 80% of the email addresses in the world for months.
Specifically email is not difficult to host because of the technical burdens but because of the black and whitelisting of the big players. Often your server IP address happens to be put on a black list without your fault and then you can write an email to Microsoft or Google and say ‘pretty please remove my IP address from your blacklist’ and they just don’t answer because they’re swamped with requests like that and they need to check each one manually or something and then suddenly you can’t email to 80% of the email addresses in the world for months.