Closed Issue: Email notifications error when updating issues [99]

The error is

2013-03-07 11:54:13,042 [19] ERROR BugNET.BusinessLogicLayer.EmailNotificationType [(null)] - Email Notification Error


System.Net.Mail.SmtpException: Insufficient system storage. The server response was: 4.3.1 Insufficient system resources
at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response)
at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception)
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at BugNET.BusinessLogicLayer.EmailNotificationType.SendNotification(INotificationContext context)

It started happening today after a few months of using BugNET. What can I do to resolve this? I am not sure where to look
Comments: unable to reproduce