* Do people running on-premises actually want us to be an intermediary for all the emails their Zulip server is sending? I would imagine if they were happy with that, they'd be happy to just use Zulip Cloud.
* How does 3CX avoid this service requiring them to do a bunch of anti-spam work?
- 3CX has a footer in each email: This email was sent from an 3CX SMTP Relay Service. If you suspect the service has been used unlawfully and/or outside the scope of delivering 3CX Phone System related emails, please file an abuse report here: https://www.3cx.com/smtpabuse
How much work this requires on their end to keep clean is unknown, but definitely a concern as well.