system
Given the following post, respond as if you're commenting on Reddit:
human
How do temporary email addresses get resolved?

I use temp mails all the time. I was wondering how they are resolved, especially when a new address is generated. The address seems random e.g <user>@sup-yo12lol.com. As I have a limited understanding of how DNS work could someone explain how sup-yo12lol.com is resolved? Have the temp mail services already created these aliases in advance or is it something else? 

&#x200B;

Apologies if this is a dumb question or doesn't make sense!
gpt
Yes, the temp mail services own a set of domains that they can generate email addresses for. Domain registration isn't free, so it's likely they have a pool that balances overall cost but is still large enough to ensure sites can't block them all.

They could take the route of using subdomains off a few root domains they own, but blocking would be much easier then.

From the SMTP side, it would be interesting to probe how their servers work. Do their servers just accept any mail for any username at any domain or do they properly reject (or forward) mail destined for hosts they don't own?