SMTP relay

What the relay is for

The SMTP relay is how your own apps send through your MailCheap account: a contact form on your site, the notifications your app sends, a script you wrote. Your app talks plain SMTP to it, with this account's username and password, and each email goes out through your account, from a domain you verified, and lands in your reports like any other email you sent.

The credential

On the SMTP relay page, create a credential: the page shows the username and a password, once. Your apps log in with them. MailCheap keeps only an encrypted copy of the password, and revoking the credential stops those apps at once, for good. Creating a new one replaces the old, which stops working that moment.

Connecting

The SMTP relay page shows the host and port to connect to. When the server has a certificate, the relay asks for STARTTLS, and your app should take it. The relay's limits: it takes the emails at the pace the server sets per account, and one email can go to 50 addresses at most.

What it can send from

An email through the relay has to come from a domain you verified on the Domains page. That way the relay is never open — nobody can use it to send from an address that isn't yours, or to burn another domain's reputation on your account.

Where the emails go

Each email the relay takes is sent through your account like one you sent in the dashboard, and counted in your reports. If you turned on the compliance archive, the relay's emails are kept there too.

On your own server

The relay is a process of its own, next to the app: run npm run smtp with SMTP_RELAY_PORT set (and, on an untrusted network, SMTP_RELAY_TLS_KEY and SMTP_RELAY_TLS_CERT). Without a certificate the relay speaks plaintext: keep it on a private network, or put it behind a proxy that does the encryption.