How to avoid conflicts with your MX records

MX (Mail Exchanger) records specify where incoming mail is delivered on behalf of a domain. Every MX value has a unique priority (also known as preference) value. The lower the number, the higher the priority.

Resend may require that you setup a MX record on two occasions:

1. Enabling your domain to send emails: You need to setup an MX record on send.example.com to establish a return-path for bounce/complaint reports from Inbox Providers. This return path is set in the email headers of every email you send through Resend.

2. Enabling your domain to receive emails: You can setup an MX record on your domain to route all received emails to Resend.

Here's an example for each occasion Resend requires you to setup a MX record.

Say you're using G Suite for your email. You'll have an MX record that looks something like this:

example.com     MX    10 alt3.aspmx.l.google.com.

This record specifies that any incoming mail to <anything>@example.com is delivered to the Google servers.

Now, say you want to use Resend to send emails from @example.com. You'll need to add an MX record for send.example.com that looks something like this:

send.example.com     MX    10 feedback-smtp.us-east-1.amazonses.com

This won't conflict because the MX record is for send.example.com, not example.com. MX records only impact the subdomain they are associated to, so the Resend MX record will not affect your existing records on the root domain.

Now say you want to start receiving emails through Resend.

Because you already have the MX record example.com, you have two options:

1. [Recommended] Create a MX record for a subdomain (e.g. subdomain.example.com). Now emails sent to <anything>@example.com will continue going to G Suite, and emails sent to <anything>@subdomain.domain.com will go to Resend.

2. Create a MX record with the lowest priority among the other MX record for your domain. Since on our example, you already had a MX record for example.com point to G Suite, you would create:

example.com    MX    9  inbound-smtp.us-east-1.amazonaws.com

Now this MX record priority has a lower value (higher priority) so it will be prioritized. But keep in mind that: