I have both a custom module and a customization to the DNN Store - that are using DotNetNuke.Services.Mail to send emails.  It works most the time, but every 12-15 times (sometimes more frequently, sometimes less frequently but about 1 in 12 has problems) there is a general exception recorded, but it doesn't get caught in my catch block so I can display anything to the user. Instead, it is found because of discrepancies in the data.  I can see the exception when I view the event viewer. 

System.IO.IOException: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host.

This is causing serious business process problems with the client as they are sporatically missing the emails they depend on to do their business.  I have tried changing the email it goes to to make sure it isn't an issue with the mailbox - and I have been in close communication with our hosting service (CrystalTech) and they have no evidence of problems on the mail server.  Thank you for any help on this urgent matter.

Carla

AssemblyVersion: 04.08.02
PortalID: 0
PortalName: My Website
UserID: 1685
UserName: fredrick
ActiveTabID: 55
ActiveTabName: Shopping Cart
RawURL: /OrderCenter/ShoppingCart/tabid/55/ctl/Checkout/mid/407/Default.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.activstyleforcaregivers.com/OrderCenter/ShoppingCart/tabid/55/ctl/Checkout/mid/407/Default.aspx
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: ba6ade2b-d76c-44d7-ba4a-870d75252333
InnerException: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Net.Sockets.Socket.Send
StackTrace:
Message: System.IO.IOException: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host at System.Net.Sockets.Socket.Send(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags) at System.Net.Sockets.NetworkStream.Write(Byte[] buffer, Int32 offset, Int32 size) --- End of inner exception stack trace --- at System.Net.Sockets.NetworkStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.Mail.SmtpConnection.Flush() at System.Net.Mail.CheckCommand.Send(SmtpConnection conn, String& response) at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, String from) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message)
Source:
Server Name: WEBE35