Error sending emails

Dear Colleagues,

We are facing an issue during email notification sent. Both SMTP server and SMTP port has been configured in the systema properties.

Also we have tried to perform a TELNET from CLM system to SMTP server and there was no error.

After creating an user account we got the error below:

In the queued messages we can see an entry with the status "awaiting retry" which corresponds to the email sent.

Any idea what could be the issue? Or any missing configuration?

Thanks in adavnce!

Regards,

Martin