How Email Delivery Actually Works

The Journey of One Email#

When you click Send Campaign in AcelleMail, a chain of events fires before the email reaches the inbox.

Step 1: The Queue#

AcelleMail adds each recipient to a Laravel queue. Queue workers pick up jobs and hand them to your configured SMTP server (or local MTA like Postfix).

Step 2: DNS MX Lookup#

Your MTA needs to find where to deliver the message. It queries DNS for the recipient domain's MX records:

dig MX gmail.com
# Returns: gmail-smtp-in.l.google.com (priority 5)

The MX record points to Google's receiving server.

Step 3: The SMTP Conversation#

Your server opens a TCP connection on port 25 (or 587/465) to Google's server:

→ EHLO mail.yourdomain.com
← 250 mx.google.com at your service
→ MAIL FROM: <bounce@yourdomain.com>
← 250 OK
→ RCPT TO: <user@gmail.com>
← 250 OK
→ DATA
→ [email headers + body]
→ .
← 250 Message accepted
→ QUIT

Step 4: TLS Negotiation#

Modern servers require STARTTLS or connect over port 465 (SMTPS). This encrypts the SMTP conversation, preventing eavesdropping in transit.

Step 5: Authentication Checks#

The receiving server runs three checks:

1. SPF — is the sending IP authorized by the From domain's SPF record?
2. DKIM — is the DKIM signature in the headers valid?
3. DMARC — do SPF and/or DKIM align with the From header domain?

All three must pass for the best inbox placement.