System.Net.WebException: The remote server returned an error: (500) Internal Server Error. asp.net, system.net.mail, authentication

System.Net.WebException: The remote server returned an error: (500) Internal Server Error. When i was trying to send email using system.net.mail the above error came. The reason for this error was i did't specify username and password along with mailmessage To sove this error you specify the username and password along with mailmessage TACS LLC Dubai Time Attendance Dubai Access Control System Gate Barrier HRMS Solutions EID Reader Software EID Reader Building Maintanance UHF Reader