XPSMTP provides a SMTP based SQL Mail solution for sending MIME based email over SMTP, implemented as an Extended Stored Procedure.
It does not require any software to be installed, just a SMTP email server that can handle the outgoing mail request. XPSMTP is using TCP/IP sockets to communicate to port 25. XPSMTP does not spawn additional threads, the xp_smtp_sendmail request is handled on the same thread as it is being called on by SQL Server. Each call to xp_smtp_sendmail establishes a connection to the SMTP server and disconnects when done sending the email. The connection is created using asynchronous communication and aborts based on a timeout value (@timeout which by default is 10000 milliseconds, so 10 seconds).