In the first instance, please ask your IT department of person in charge of SQL to restart your SQL server, as issues of this nature are often caused by issues with resource availability on your server. Restarting the server will release resources back to the system and should alleviate your issues.
Please check to make sure your mail server is not causing the issue. If the mail server has too many outstanding updates on it, this can be the cause of the performance issue.
Check also if your database has been re-indexed recently, if it hasn't re-indexing will also improve performance of the system.
