From: DeskNow Knowledge Base
http://www.desknow.com/kb/

Socket exception: Connection reset
http://www.desknow.com/kb/idx/11/193/article/

If you receive a bounce email with this error, it means that the SMTP connection that DeskNow tried to create to send out your email was suddenly closed.

If this only occurs when sending emails to a specific domain

This typically indicates that the recipient domain has blacklisted your IP address, and believes that you are a spammer. Contact the mail administrators of that domain to verify your status.

If this occurs when sending to different domains

This typically indicates a network issue in your environment. This could be a problem in your firewall/router, or on the server where DeskNow is running. By far the most common cause of this problem is antivirus software with the 'email scanning' functionality enabled. This functionality tries to intercept SMTP traffic, and scan emails as they pass through. Often these software are designed to filter traffic coming from a single mail client such as Outlook, and not a multitasking mail server. Since DeskNow can already scan all your outgoing mail, disable any 'email scanning' functionality in your antivirus/internet security/anti malware software.