[spectralblu]

This sounds a lot like Throttle (https://throttlehq.com/). How are they getting around the deliverability issues? If they forward mail along, don't large ISPs like Gmail ultimately attribute any spam that comes along to their outbound IPs?

I moved away from Throttle for this very reason, because getting mail deliverability right is incredibly finnicky. Ended up moving to Fastmail and using their catchall. Fastmail solved the deliverability problem for me (since they host the catchall domain), as well as permitting me to send out from any of my wildcard aliases (thus allowing me to reply in situations where I still want to keep my real address hidden).