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IP authentication lets a single trusted IP address send through an SMTP user without supplying the username and password. It’s intended for the rare case of a device or appliance that can’t perform SMTP AUTH at all, such as a network printer, scanner, or legacy appliance.
Only use this if you absolutely have to. IP authentication removes username and password from the equation entirely. Anything sending from the allowed IP is trusted to relay mail. Prefer normal username and password authentication, optionally combined with IP restrictions, wherever the sending device supports it. Reach for IP authentication only when a device genuinely cannot authenticate, like a printer or appliance with no AUTH support.

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How it works

You still create a normal SMTP user with a username and password. IP authentication is an additional option on top of that user: you nominate a single IP address, and connections from that IP are allowed to send without presenting the username or password. The username and password still work; they’re simply no longer required when connecting from the allowed IP. This means the same SMTP user can be used normally by apps that authenticate, while a single appliance that can’t authenticate relays from the nominated IP.

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Set it up

  1. Create an SMTP user with a username and password as usual.
  2. Open the SMTP user in the dashboard under Outbound → SMTP.
  3. Scroll to the bottom to the IP authentication setting.
  4. Enter the single IP address the device sends from.
  5. Save.
The device can now connect to relay.jetsmtp.net from that IP and send mail without authenticating.
An IP can only be assigned to one SMTP user at a time. Each IP address is unique across the whole platform, so if it’s already set on another SMTP user (in your account or anyone else’s), you won’t be able to add it again. Remove it from the original user first, then assign it where you need it.

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When to use it

Use IP authentication only when the sending device can’t perform SMTP AUTH:
  • A network printer or scanner that emails scans but has no field for a password.
  • A legacy appliance or piece of hardware with no authentication support.
For anything that can authenticate (apps, scripts, mail servers, control panels), use a normal username and password. If you also want to lock that credential to known servers, add an IP restriction; it limits where the credential can be used without giving up authentication entirely.