Very often, an SMTP error message is just a mystic number in a form of incomprehensible code. You realize you have an SMTP error and receive a SMTP error code but in fact, it means nothing to you if you do not understand what an SMTP error number stands for and what it means.
SMTP Error Numbers
SMTP error numbers each has their own meaning and mail servers reply to every request with a return code. This return code consists of numbers and means the following:
The first number usually tells if a server has accepted a command and if it handled it correctly. The values in the first number usually are:
1 – Server accepted command, but no action is taken and a confirmation message is required.
2 – Server completed the task.
3 – Server understood request, requires further information in completing it.
4 – Server encountered a temporary failure, repeat command without changing it as servers often uses temporary failures to stop untrusted senders from entering a server.
5 – Server encountered an error.
The second SMTP error numbers gives a lot more information and the values used includes:
0 – syntax error occurred
1 – Indicates that informational reply is available such as a help request
2 – Refers to the status of the connection
Numbers 3 and 4 are unspecified
Number 5 refers to the mail system status as a whole as well as the mail server
The last of the SMTP error numbers are the detailed specifics and the lots of graduations of a mail transfer status. This is where the SMTP error codes comes in as they are explained in the SMTP error list below. SMTP Error List
SMTP Error List
211 -system status message
214 -help message follows
220 – SMTP service ready
221 – SMTP service closes
250 – Action requested is takes and complete
251 – recipient is not local, but server will accept and forward a message
252 – recipient can't be VRFYED, server still accepts and will attempt delivery of email
354 -message input and end must be with .
421 – no service available and connection to be closed
450 – command failed due to unavailable mailbox
451 – Server error that is not your fault and command aborted.
452 – command was aborted due to insufficient system storage on server
500 – command is not recognized due to syntax error
501 – command arguments has syntax error
502 – command not implemented
503 – bad sequence of commands was encountered
504 – unimplemented command parameter
550 – command requested failed as no user mailbox was available
551 – recipient is not local and server gives forwarding address to try
552 – actions aborted due to invalidity of mailbox name
554 – transaction failed