Common SMTP Email Failures
Introduction
Simple Mail Transfer Protocol (SMTP) is a protocol used for sending emails. Despite its widespread use, users often encounter various issues when sending emails via SMTP. This article addresses some of the most common SMTP email failures and provides solutions to resolve them.
Common SMTP Email Failures and Solutions
This article provides some reasons for undelivered emails via SMTP.
Response
Action
Bounced Address
550 Invalid Recipient
Recipient email address is invalid
550 5.4.1 Recipient address rejected: Access denied
Sender blocked by recipient
550 DMARC Sender Invalid
Ensure all the IP addresses for your mail servers are listed in your SPF records. - Link
550 RCPT TO:<a@a.com> User unknown
Email address does not exist
unable to get mx info: failed to get IPs from PTR record:
This is a DNS issue or, more likely, a typo in the email address.