Can't send mails

Hello.
I have a website written in aspnet and I noticed that visitors can't send me an email.
There is no error, but no email either.

I did change the way mails are sent, by creating new mail in control panel and setting that mail as an authentication and at that time, it worked.
Am I missing something more?

To inform you, I've created a ticked, but I have to say that my ticket system is sent to my colleague and then he has to open a ticket again, so this ticke I opened might not reach you.