Common SMTP Error Codes and Their Meanings

SMTP (Simple Mail Transfer Protocol) is the standard protocol used for sending emails. Here are some of the most common SMTP error codes and what they indicate:

• 421 - Service not available: This error code indicates that the mail server is currently unavailable, often due to maintenance or overload.
• 450 - Requested mail action not taken: This code means that the recipient's mailbox is unavailable or could not be found.
• 550 - Requested action not taken: This code typically indicates that the recipient's email address is invalid or the mailbox is full.
• 554 - Transaction failed: This error code is often triggered by spam filters or if the recipient's server is rejecting the email.

Understanding these common SMTP error codes can help troubleshoot email delivery issues and ensure a successful communication process.