Using Multiple SMTP servers

If your Customer.io subscription is on the Premium plan, you can configure multiple custom SMTP servers to have greater control over your deliverability.

Getting started

First, you will need to configure your primary custom SMTP server. By default your first custom SMTP server will be set to send all your Customer.io email messages.

Single SMTP server.png
Single SMTP server.png

Customizing campaign delivery

To customize the delivery settings by campaign type, you need to add your additional servers in the same manner as you added your first custom SMTP server. Once this is done, your new servers default to sending emails for None.

Additional SMTP servers.png
Additional SMTP servers.png

This means the new servers will not send any Customer.io generated emails. To change that, set them to one of the following options from the drop-down:

  • Segment Triggered: Sends emails for your Segment-Triggered Campaigns
  • Event Triggered: Sends emails for your Event-Triggered Campaigns
  • Newsletters: Sends emails for your Newsletter Broadcasts
  • Triggered Broadcasts: Sends emails for your API Triggered Broadcasts

It’s mandatory for at least one of your custom SMTP servers to stay set on All Emails. This is the server Customer.io will fall back to for any campaign types that don’t have a specific server specified.

If you have any questions about configuring multiple SMTP servers that weren’t covered here, get in touch with us!