I use exactly this on my personal (free) and work (paid workspace) accounts. I got an official notification from Google that one member in my workspace (me) has used the feature in the last 30 days and will be affected. I didn't (yet) get a notification on my personal account.
I also rely pretty heavily on this feature for a few very low traffic domains that I need but only have super set up on super clunky web mail, so I guess I'm in the market for a new mail client :(
Maybe you can automatically forward mails from that domain to Gmail and find a way to label them.
At worst you can write a mail client to do that by logging in, listing mails, mailing them to you and keeping track of what it already sent (sqlite?) They are very well known protocols with plenty of implementations, so probably a LLM can write the code with not much guidance.
I also rely pretty heavily on this feature for a few very low traffic domains that I need but only have super set up on super clunky web mail, so I guess I'm in the market for a new mail client :(