Error: SMTP Error 551

What's Causing This Error

SMTP error 551 occurs when an email bounces during the delivery process. Two types of bounces may take place:

1. Soft Bounce - Soft bounce takes place when the recipient's mailbox is full or if their email server is temporarily unavailable
2. Hard Bounce - Hard bounce occurs when the email address is invalid or if the mail server attempts to deliver the email to another server that does not handle the recipient's email address.

The reason behind this error code may not always be clear and other reasons can also contribute to causing an email to bounce.

Solution - Here's How To Resolve It

To resolve this error, ensure no underlying issues affect the email server or the connectivity.

The following common troubleshooting steps can help narrow down and resolve the issue at hand:

1. Ensure that all recipient's email addresses are valid.
2. Ensure that the recipient has enough space in their mailbox to receive the email.
3. Ensure that the recipient's email server is available and is accepting email.