Which of the following answers are true about SMTP$?$

a$.$

The Simple Mail Transfer Protocol $($SMTP$)$ is used to transfer mail reliably and efficiently.

b$.$

Using SMTP$,$ a process can transfer mail to another process on the same network or to some other network via a relay or gateway process accessible to both networks.

c$.$

None of the above.

d$.$

Both a and b$.$