This page lists the most common email error codes used by TECH 2U
If you have been referred to this page by an error code we suggest finding the code below and then actioning accordingly.
SMTP Codes (Errors et al.)
SMTP codes consist of three digits, for example, 550, 551, 221, 354, etc. Not all of them mean an error although most people are only interested in those that do. In order to understand how these codes work, you have to know that each digit (the first, the second and the third) have their own meaning.
The first digit tells you if your command was accepted and processed. There are five different values for that:
1. Mail server has accepted the command, but does not yet take any action. A confirmation message is required.
2. Mail server has completed the task successfully without errors.
3. Mail server has understood the request, but requires further information to complete it.
4. Mail server has encountered a temporary failure. If the command is repeated without any change, it might be
completed. Try again, it may help!
5. Mail server has encountered a fatal error. Your request can't be processed.
As you can see, the codes that start with 4 and 5 are the ones that tell you that your message won't be sent until you find and fix the problem.
The second digit tells you more
0. Syntax error
1. Information reply (for example to HELP request)
2. This digit refers to the status of connection
3. This digit refers to the status of the mail server
4. Not used
5. Not used
The third (last) digit of the code tells you the details of mail transferring status. | 
