I've developed an application in C# that can send emails with attachments.

This has usually worked fine but I've seen timeout errors over the past few days:

System.Net.Mail.SmtpException: Failure sending mail. ---> System.Net.WebException: The operation has timed out.     at System.Net.Mail.SmtpConnection.ConnectAndHandshakeAsyncResult.End(IAsyncResult result)     at System.Net.Mail.SmtpClient.ConnectCallback(IAsyncResult result)     --- End of inner exception stack trace ---

Why is this??