Use Your Own SMTP Server
By default, Customer.io takes care of your email delivery. However, you can optionally tell Customer.io to send mail through any other SMTP server.
- You’re in full control.
- We won’t charge you anything based on the volume of email you send. You’ll only pay the plan cost based on the number of profiles in your account.
- We’ll still handle your open and click tracking.
- We’ll keep a full copy of your sent emails associated with the recipient.
- Customer.io won’t have a feedback loop for data from your email service provider.
- Data about delivered, bounced and spammed emails won’t be visible in Customer.io. We have integrations providing delivered, spam and bounce data with Mailgun, Mailjet, Mandrill, Sendgrid and Sparkpost
If your SMTP server uses an IP allowlist, allowing only specific IP addresses to connect you’ll need to allowlist Customer.io IP addresses prior to configuring custom SMTP in the application.
Use the correct IP addresses for your account region.
|US IP addresses||EU IP addresses|
This list is subject to change
If you haven’t added a Sending Domain yet, you’ll need to do that before you can send email from Customer.io.
When using custom SMTP, you do not need to authenticate your domain in Customer.io. However, you should check your custom SMTP provider’s documentation to see if you still need to add DNS records (such as SPF and DKIM) to your domain to use their services successfully.
Branded link tracking with custom SMTP
Due to a limitation with our cloud provider, you cannot send SMTP messages using port 25. Major SMTP providers normally allow delivery using port 465, 587 or 2525 (like in our screenshot above). If you need alternatives, consult your delivery provider’s documentation for ports that work with their service. Regardless of port used, we always initiate a TLS connection (via the STARTTLS command, when supported by your provider), to ensure the security of your outbound messages.
If you have Premium Customer.io plan, you can add additional SMTP servers to segment deliveries by campaign type. For details check out our documentation on configuring multiple SMTP accounts.
If you have any questions about setting this up, get in touch!