Symptom: the MX record looks right in your provider's panel but Resend keeps failing it.
1. Confirm the cause: check the actual public value with nslookup -type=MX on the send subdomain. If you see your own domain glued on the end (e.g. feedback-smtp.eu-west-1.amazonses.com.example.com instead of feedback-smtp.eu-west-1.amazonses.com), your provider auto-appends the domain name.
2. Fix: in your DNS provider, edit the MX value to end with a trailing period, e.g. feedback-smtp.eu-west-1.amazonses.com. with the dot. The trailing period marks it as a fully qualified domain name that must not be modified.
3. The region in the MX value matters: it may be us-east-1, eu-west-1, ap-northeast-1, or sa-east-1 depending on your domain's region. Copy the exact value from your domain's DNS records table.
4. The same trailing-period trick applies to CNAME values when the provider shows the Resend host with your domain appended.
5. Verify: re-run the nslookup and confirm the public value now matches Resend exactly, then hit "Restart verification" in the dashboard.