MX records without breaking your primary domain

Operations

Your main company domain probably already has mail. Here's how to add myagentmail without blowing up your existing inbox.

The problem

A domain can only have one set of MX records. If you point yourcompany.com's MX at myagentmail, all mail for yourcompany.com — including your existing [email protected] inbox — starts flowing into myagentmail, and your Google Workspace/Outlook/Fastmail inbox goes dark.

The fix: use a subdomain

Register the domain as mail.yourcompany.com (or agents.yourcompany.com, or any subdomain that isn't already in use) instead of the apex:

curl -X POST https://myagentmail.com/v1/domains \
  -H "X-API-Key: tk_..." -H "Content-Type: application/json" \
  -d '{"domain": "mail.yourcompany.com"}'

MX records for a subdomain are completely independent of the apex. Your [email protected] inbox keeps working at its existing provider; mail to [email protected] routes to myagentmail.

What to set

In your DNS editor, under the mail subdomain, add exactly what the domain verify response gives you:

MX: mail.yourcompany.com. IN MX 10 mail.myagentmail.com.
TXT DKIM: the long RSA record on the selector hostname we return
CNAME bounce handler: on bounce.mail.yourcompany.com.

Why not just use the apex?

You can, if the apex has no existing MX or you're migrating away from another provider. But for most existing businesses the apex is load-bearing and a subdomain is a zero-risk move. SPF and DKIM alignment still work correctly for subdomain sends; DMARC aspf=r / adkim=r (relaxed alignment, the default) treats subdomains as aligned with the organizational domain.