Restricted access denied, system.net.mail

Question

We have an aspx.net site that sends mail to users using a web server hosted externly.

This works fine for several years, sending 100-1000 letters per day, but recently, users began to report that they do not receive mail - in a few days they receive all letters (2-100) and only a few days 40-60% .

All letters are formatted the same and have the same content (with the exception of some dynamic fields, such as name, password, etc.).

I looked through my error log and now I see this error when letters are lost:

system.net.mail.smtpexception: transaction failed the server response was: <[e-mail]> Relay access denied

Any feedback will be assigned.

Regards and happy coding, Thomas

Answer 1

"Denying access to relay" is usually caused either by the fact that the mail server does not recognize the domain domain.tld in the address of the senders, therefore, does not send mail on their behalf, or because the server requires SMTP authentication that was not provided.

Answer 2

The server that is trying to send the message requires authentication from mail sent by SMTP. Try using your domain credentials to send mail.

Answer 3

SMTP- .