Definition
Every email passes through an SMTP server at both the sending and receiving ends. Understanding SMTP helps diagnose bounces and delays.
Best Practices
- Know your outgoing SMTP host and port.
- Watch SMTP reply codes when sends fail.
- Ensure your SMTP server is authenticated and well-configured.
Was this useful?
Related Glossary Terms
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
Email Authentication Protocols
Email authentication protocols are technical standards that verify the identity of an email sender, helping mailbox providers distinguish legitimate mail from spam and phishing.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Classification
Bounce classification uses SMTP codes (550, 551, 552, 553, 554, 450, 451, 452) and enhanced status codes to categorise permanent and transient delivery failures.
Frequently Asked Questions
A server that sends and relays email using the SMTP protocol.
Port 25 for relay, 587 for submission, and 465 for implicit TLS.
Reply codes tell you whether a message was accepted or rejected.