After a successful SMTP session, what command is typically used to end the connection?

The command typically used to end an SMTP session is "QUIT." This command signals the client to terminate the connection with the SMTP server gracefully. When the server receives a "QUIT" command, it can complete any outstanding messages or tasks and then close the connection in an orderly fashion, allowing for proper cleanup of resources.

This aligns with the SMTP protocol's design, which emphasizes clear communication between the client and server. The "QUIT" command is defined in the protocol specifications, making it the standard method of concluding a session once all desired email transactions have been completed.

In contrast, the other commands listed—such as "BYE," "FIN," and "END"—are not recognized as proper commands for terminating an SMTP session. They do not conform to established SMTP protocol standards and therefore would not be effective in closing the connection in this context.