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SMTP Error: Please authenticate before sending email

The following shows the typical error from the SMTP session using mail client such as Outlook or Outlook Express:

 The message could not be sent because the server rejected the sender's e-mail address. The sender's e-mail
 address was user@domain.tld . Subject 'Subject', Account: 'mail.domain.tld', Server: 'mail.domain.tld',
 Protocol: SMTP, Server Response: 451 user@domain.tld please authenticate before send', Port: 25, Secure(SSL):
 No, Server Error: 451, Error Number: 0x800CCC78

The error occurs due to user was trying to send the email out without being authenticated first by downloading with POP3 or login with Webmail.


  • Download the email first to get authenticated, don't just click on the “Send/Recv” button on Outlook Express. Instead, click and hold on the “Send/Recv” button, select “Receive All” first.
  • Or, you may turn the SMTP authentication ON in your profile and use port 587.
faq/email/smtp_error_please_authenticate_before_sending_email.txt · Last modified: 2015/07/28 16:05 by vikki