MX record

An MX (mail exchanger) record tells the world where to deliver mail for your domain. Each record has a priority number and a server name. Senders try the lowest number first and fall back to the next one if it does not answer.

MX records are about receiving mail, but they matter for sending too. A domain with no working MX looks suspicious to receivers. Replies and bounce messages to your cold email also need a place to arrive. If the MX is wrong, you will not see replies and you will not learn about bounces.

Common mistakes: setting up a new secondary sending domain and never adding MX records, leaving old MX records from a previous provider next to new ones, or pointing MX at a name that is a CNAME. Each sending domain needs MX records that match the mailbox provider you actually use. Check them after any DNS change.