Troubleshooting SQL Mail: SQL Mail Stops Responding
The most common cause of this problem is a temporary loss of the network connection to the e-mail server. This problem most often occurs when SQL Mail is configured to use Internet protocols for message delivery, although it can also occur when communicating with a Microsoft Exchange host.
When SQL Mail loses a connection to the e-mail server, the Extended MAPI components display a message that requests user action as to whether or not to continue. This message does not appear on the server because SQL Mail is run from the SQL Server service. Because the message does not appear, there is no way to respond to the message to allow SQL Mail to continue. Even if the network connection becomes available, SQL Mail does not retry the connection.
To work around the problem, you must stop and restart SQL Server.
To resolve the problem, update your applications to use Database Mail. Database Mail does not use the extended MAPI protocol, and is designed to gracefully recover from lost connections without user intervention.