Their keys
A key for one client can’t read another’s mail.
Client A
ss_live_4f2a… send onlyClient B
ss_live_81cd… send, readClient C
ss_test_09be… test projectA project per client, each with its own domain, keys and limits.
mail.client-a.comDevelopersend.client-b.ioRead-only clientmail.client-c.orgDeveloperA key for one client can’t read another’s mail.
ss_live_4f2a… send onlyss_live_81cd… send, readss_test_09be… test projectKnow who used what before you invoice.
A hard cap protects the whole agency.
At the cap, sending stops. You are never billed beyond it.
Invite a client by email and pick the projects they can see. “Did my password reset go out?” answers itself.
Every key, invite and limit change is written to an audit log. Secrets never are.
Client seats are included on Scale and Enterprise. Everyone signs in with an emailed link: no shared passwords.