Email outbox, email contact list, email templates, sent message ID tracking, and the first AI touch on email: AI auto-responder on inbound messages. Five migrations across the day. Biznetrix now has both a chat layer and an email layer, both with AI response capability.
The design decision I am happiest with: email contacts and chat contacts both link back to the same CRM contacts table. There is no separate "email list" and "chat contact" — they are the same person viewed through different channels. This will matter a great deal later when cross-channel attribution is needed.