SMTP Test Tool

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For local network SMTP test use our SMTP Diag Tool

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