IMHO, there are two components to "email" that do not necessarily need to be connected
1. receving mail
2. sending mail
Only #2 became difficult
Internet subscribers receive lots of email to which they never reply
Sometimes "throwaway" disposable email addresses are useful^1
Various third parties offer this as a "service", i.e., #1 is disconnected from #2
Self-hosting #1 can provide an alternative to using third parties
Generally, the only cost is a domain name registration
1. Also HN commenters have complained in the past that email sent via self-hosted SMTP to certain recipients, e.g., Gmail recpients, may end up stored on certain undesirable third party servers. This is because the recpient uses a third party for both #1 and #2, a so-called "email provider"
1. receving mail
2. sending mail
Only #2 became difficult
Internet subscribers receive lots of email to which they never reply
Sometimes "throwaway" disposable email addresses are useful^1
Various third parties offer this as a "service", i.e., #1 is disconnected from #2
Self-hosting #1 can provide an alternative to using third parties
Generally, the only cost is a domain name registration
1. Also HN commenters have complained in the past that email sent via self-hosted SMTP to certain recipients, e.g., Gmail recpients, may end up stored on certain undesirable third party servers. This is because the recpient uses a third party for both #1 and #2, a so-called "email provider"