SMTP Test Tool
The SMTP Test can help you identify where your send mail request is encountering
issues.
Depending on the mail server, you’ll receive a series of responses, possibly
with comments to help explain them.
There are also a number of SMTP codes:
Code: 220 - Message: Service ready
Code: 221 - Message: Service closing transmission channel
Code: 250 - Message: Requested mail action okay, completed
Code: 251 - Message: User not local - forward to [path]
Additionally, there are a few common SMTP error codes as well:
Error: 450
- Mailbox unavailable
Error: 451 - Local error in processing
Error: 451 - Insufficient system storage
Error: 500 - Syntax error (command unrecognized)
Error: 501 - Syntax error (bad parameter or argument)
Error: 521 - Domain does not accept email
Error: 535 - Authentication unsuccessful (bad username or password)
Error: 530 - Access denied
Error: 554 - Relay Access denied