Providers
Send & Retain delivers your mail by default; Resend or SendGrid can share the load. Everything above delivery is ours.
A provider is the delivery backend for a project. By default that is Send & Retain's managed sending — no account to create, no key to rotate. You can also add your own Resend or SendGrid key alongside it. Either way, Send & Retain owns everything above delivery: templates, contacts, automations, suppression, unsubscribe, the message log, and metrics.
Managed sending
Managed sending is the default and needs no credentials. It starts on a small daily volume and warms up automatically to protect your reputation; the Settings → Sending page shows where it is on the ramp. Sending is metered by volume — contacts are unlimited.
Your own Resend or SendGrid key (optional)
Already sending transactional mail through Resend or SendGrid? Add one of them on the same page. With both connected, traffic splits per message, and a message that fails on one provider is retried on the other. One Resend or SendGrid key per project.
One abstraction
Feature code never talks to a provider directly — all sends go through one
internal abstraction, so the provider mix doesn't change how you use the API.
The same POST /api/v1/emails works whichever provider delivers a message.
Credentials
A Resend or SendGrid API key is per-project and entered only in the dashboard under Settings → Sending. It's validated against the provider and stored encrypted. It never travels through the API, chat, or MCP, and is never logged. Managed sending has no key at all.
Domains and senders
Sending requires a verified domain and a sender on it. A from-address that doesn't resolve to a verified domain is rejected before send. See Connect sending.
Webhooks
Each provider reports delivery events back to the project, verified before they're trusted (Svix HMAC for Resend, ECDSA for SendGrid). These drive message status and automatic suppression. See Webhooks.