LE doesn't need any A or AAAA record. The domain must exist in the DNS and you must be able to create records in the domain.
If you're using internet mail you have a domain, so you can do this. The time for self-signed certificates has passed.
Software is a collective. A billion or so people get the same software. The time for self-signed certs has passed because supporting that in software for a billion people opens up some of that billion to attack.
The few people who understand the niceties of certs can create a private CA, trust that, and use that CA to sign a regular cert. Doing that is nontrivial, but it doesn't put other people at risk.
A pinned self cert is still more secure than this because you don’t have to trust any CAs.
> The time for self-signed certificates has passed.
This is bad blanket advice and very much depends on use-case.