Sharepoint 2010 / SMTP Server (IIS 6.0)

Hello

Since a few days we receive no mails from our Sharepoint 2010 Server. Before it was working without problems-

I've restared all SharePoint and IIS 6.0 & 7.0 Services. But it isn't working. If I try to send a mail via telnet then I receive a email.

I noticed also that the mails from the SharePoint Server are not in the queue or drop folder from the SMTP-Server: C:\inetpub\mailroot\

Where are the mails landed? Is there a queue from the SharePoint-Server or a log which I can check?

Thank you for your help.

Best regards

nsithampary