After sending an email, you receive a bounce message, indicating that the message was not delivered to the intended recipient. There can be many reasons for this, so we will cover the most common reasons in this article.
You receive a message similar to the following, with a "503" error:
From: System Administrator
Sent: Saturday, July 19, 2008 5:03 PM
To: Joe Smith
Subject: Undeliverable: Your subject here
Your message did not reach some or all of the intended recipients.
Subject: Your subject here
Sent: 7/19/2008 5:02 PM
The following recipient(s) could not be reached:
'firstname.lastname@example.org' on 7/19/2008 5:03 PM
503 Valid RCPT command must precede DATA
Most outgoing mail servers today require authentication before allowing your email to go through. This helps prevent people from sending mail through a server that they do not have an account on.
To solve this problem, you simply need to go into your email client (e.g. Outlook), look for the Outgoing Mail Server settings, and check the box that indicates "My outgoing mail server (SMTP) requires authentication" or words to that effect.