What happens when you press “Send”?

You click Send. What happens next?

Your email doesn't teleport to the recipient. It hops through several servers, each one checking credentials and routing the message forward. The whole process takes seconds, but there are 5 distinct steps happening behind the scenes.

Step 1: Your email client talks to your submission server. Whether you're using Gmail, Outlook, Fastmail, or a marketing platform like Mailchimp, your email client hands the message to a submission server (usually running on port 587). This server checks your login credentials. If you're not authenticated, the message doesn't go anywhere.

Step 2: The submission server wraps your message in an SMTP envelope. Think of this like putting a letter in a postal envelope. The SMTP envelope contains routing info (who it's from, who it's going to) separate from the message headers your recipient will see. This is why reply-to addresses and return-path addresses can be different from the visible "From" line.

Step 3: DNS lookup for the recipient's mail server. Your server needs to know where to deliver the message. It queries DNS for the recipient domain's MX record, which points to the receiving mail server. If there's no MX record (or if DNS fails), the email bounces immediately.

Step 4: Your server connects to the recipient's server. Once it knows where to go, your sending server opens an SMTP connection to the recipient's mail server and transmits the message. The receiving server might accept it right away, or it might queue it for spam filtering first. This is where SPF, DKIM, and sender reputation checks happen.

Step 5: The recipient retrieves the message. The email sits on the receiving server until the recipient's email client pulls it down (via IMAP or POP3) or they log in to webmail. This step can happen instantly if they're online, or hours later if they're not.

One last thing: just because the recipient's server accepted your email doesn't mean it landed in the inbox. The receiving server might still route it to spam, or the recipient's filters might move it to a folder. Delivery and inbox placement are two different things.

But if you want to understand what happens during that server-to-server handoff in Step 4, read how an email travels from one server to another. And if you're curious about the protocols that make all this work, start with SMTP, POP, and IMAP.