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The Typical Email Flow: How Emails Are Processed

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The Typical Email Flow: How Emails Are Processed

The Typical Email Flow: How Emails Are Processed

Every email your users send takes the same journey through a handful of servers and checks. If you run a mail platform, knowing each step tells you where delays occur, where spam is blocked, and where to look when something breaks.

Understanding How Emails Are Processed

Between “Send” and the recipient’s inbox, an email passes through four types of software:

  • Mail user agent (MUA): the email app or webmail the sender and recipient use.
  • Mail submission agent (MSA): the provider’s server that accepts mail from logged-in users, usually on port 587.
  • Mail transfer agent (MTA): the server software that moves mail between organizations using SMTP (Simple Mail Transfer Protocol).
  • Mail delivery agent (MDA): the software that places the message in the recipient’s mailbox.

The Stages of Email Processing Explained

  1. Sender initiation: The sender clicks “Send”. Their email app submits the message to their provider’s server, which checks that the user is logged in.
  2. Outbound checks: A well-run provider scans outgoing mail for spam and signs of compromised accounts before it leaves the network. Here’s how inbound and outbound protection differ.
  3. DNS lookup: The sending mail transfer agent looks up the MX record of the recipient’s domain to find which server accepts its mail.
  4. SMTP connection and reputation check: The sending server connects to the receiving server. Before accepting anything, the receiving server checks the connecting IP address, often against DNS blocklists. Learn how blocklists work.
  5. Email authentication: The receiving server checks SPF, DKIM, and DMARC to confirm the sender is allowed to send for that domain. Read our guide to SPF, DKIM, DMARC and BIMI.
  6. Content filtering: Spam and malware filters scan the message content, links, and attachments. See how spam filtering works.
  7. Delivery: The mail delivery agent places the message in the inbox or the spam folder. If the message fails a check, it may be rejected, and the sender gets a bounce message. Find out why emails bounce.
  8. Reading: The recipient opens the message through IMAP, POP3, or webmail.

Key Steps in How Emails Are Processed

For security, three steps matter most: the reputation check at connection time, authentication, and content filtering.

The earlier you stop a bad message, the less it costs you. Rejecting spam at the connection stage means your server never has to download, store, or scan it.

Why Email Processing Matters

Knowing the flow helps you in three ways:

  • Troubleshooting: When mail is delayed or bounced, you can pinpoint the stage at which it failed.
  • Security: You can see where to add protection, and where attackers try to slip through.
  • Deliverability: Outbound checks keep your own IP addresses off blocklists, so your users’ mail keeps arriving.

Get Started with Email Security

Start by reviewing what your mail servers check at each stage. Abusix Mail (formerly known as Guardian Mail) adds real-time IP, domain, and URL blocklists at the connection and content stages, so you can reject most spam before it reaches your filters. See how Abusix Mail works.

Learn More

Talk to Abusix. Book a call here.

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