Common SMTP commands include:
| Command | Purpose |
|---|---|
| EHLO | Identify client and request ESMTP capabilities |
| HELO | Basic SMTP greeting |
| MAIL FROM | Set envelope reverse-path |
| RCPT TO | Add envelope recipient |
| DATA | Begin message content |
| RSET | Reset current transaction |
| NOOP | No operation / request reply |
| QUIT | End session |
| VRFY | Request address verification where supported |
Extensions add commands such as STARTTLS and AUTH.
Servers commonly restrict or disable information-revealing behavior such as VRFY.