Relay access denied, system.net.mail

Question

We have a aspx.net site which send out mail to users using a web server hosted externly.

This have been working perfectly for a couple of years sending 100-1000 mails pr day, but recently users have started to report that they do not recieve mails - some days they recieve all mails (2-100) and some days only 40-60%.

All mails are formatted equal and have the same content (except for some dynamic fields like name, password etc).

I've looked at my error log and now I see this error when mails are lost:

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

Any feedback would be appriciated.

Regards and happy coding, Thomas

Solution

"Relay access denied" is usually caused either because the mail server doesn't recognize the domain.tld domain in the senders address so wont send mail on their behalf, or because the server requires SMTP authentication which was not provided.

Comments

[Muleskinner]

thank you for your input, but how can this explain that messages, with same sender, same reciever and (almost) same content sometimes are recieved successfully and sometimes not?