[arp242]

There's a limit of 100 domains, plus 1 for every user in the account.

https://www.fastmail.help/hc/en-us/articles/1500000277382-Ac...

Probably mostly there to prevent rampant abuse from spammers, scammers, or people just doing really weird shit creating millions of $thing where everyone else has a few dozen or hundred.

[selykg]

That seems reasonable. But nice catch. I didn’t know that limit existed. I have 6 lol. Long way to go before that limit impacts me