Answer:
HELO/EHLO.
Step-by-step explanation:
Simple Mail Transfer Protocol (SMTP) is a protocol followed while sending an electronic mail or receiving it. It is a TCP/IP protocol (a protocol used to interconnect in communication protocols).
To test Simple Mail Transfer Protocol (SMTP), the HELO/EHLO command is used. There are several other commands in SMTP, which is used to communicate properly.
The HELO command is a type of command in SMTP which is used to test or initiate SMTP communication. HELO/EHLO are the commands which are used to test SMTP communication. They are used interchangebaly.
Thus the correct answer is HELO/EHLO command is used to test SMTP support.