What is a mail server?

A mail server is a computer that handles the technical work of sending, receiving, and storing email. When you send an email, your mail server connects to the recipient's mail server and hands off the message. When someone emails you, their mail server delivers it to yours, where it sits until you open your inbox.

Mail servers use specific protocols to do their job. SMTP (Simple Mail Transfer Protocol) handles outgoing mail and server-to-server transfers. IMAP (Internet Message Access Protocol) and POP3 (Post Office Protocol) handle how you retrieve messages from the server to your device. SMTP pushes mail out, IMAP and POP3 pull it in.

If you use Gmail, Outlook, or Yahoo Mail, you're connecting to their mail servers. When you check email on your phone, you're pulling messages from a mail server (usually via IMAP). When you hit send, your device talks to an outgoing mail server (SMTP) to relay the message.

For most people, "mail server" just means Gmail's servers or Outlook's servers. You don't run one yourself. But if you're sending marketing or transactional email for a business, you're either using an Email Service Provider (like Mailchimp or SendGrid) that runs mail servers for you, or you're configuring your own outgoing mail server (which means setting up SMTP, DNS records, and authentication).

The confusion most senders hit: "Do I need to set up a mail server?" Usually no. If you're using an ESP, they handle the mail server. If you're sending through Google Workspace or Microsoft 365, same thing. You only configure your own mail server if you're running email infrastructure in-house or using a relay service like Mailgun or AWS SES.

Next step: If you're trying to figure out whether you need your own mail server or an ESP, check out what an ESP actually does. If you're debugging delivery and need to see how mail servers talk to each other, read what happens when you press Send.