Basic Technical Aspects of Email Delivery

SMTP (Simple Mail Transfer Protocol) Basics

SMTP is the protocol responsible for transmitting emails over the internet. From an ESP perspective, best practices include:

• Properly configured Mail Transfer Agents (MTAs) to ensure smooth email sending.

• Authentication using SPF, DKIM, and DMARC to prevent spoofing and improve deliverability.

• Monitoring SMTP responses to detect issues like blocked emails or throttling by ISPs.

Understanding MX Records and DNS

MX (Mail Exchange) records define the mail servers responsible for receiving emails for a domain. ESPs should:

• Ensure accurate MX record configuration to avoid delivery failures.

• Use PTR (reverse DNS) records to verify sending servers, reducing spam flags.

• Maintain a valid SPF record to list authorized sending servers.

Throttling and Rate Limiting

ISPs often limit the number of emails an ESP can send within a certain period. To optimize delivery:

• Implement adaptive sending speeds based on recipient engagement and ISP feedback.

• Segment large campaigns to avoid triggering rate limits.

• Use retry policies for soft bounces, with exponential backoff strategies.

Handling Feedback Loops (FBLs)

Feedback loops allow ESPs to receive reports when recipients mark emails as spam. Best practices include:

• Registering for FBLs with major ISPs to receive complaint notifications.

• Automatically removing complainers from mailing lists to improve sender reputation.

• Analyzing FBL data to identify problematic email content or audience segments.