On which servers should the port for SMTP be open?

Domain controllers

Email servers

File servers

Web servers

SMTP should be open on Email Server

Explanation:

SMTP is used for the purpose of delivering email. It is the short form of simple mail transfer protocol. It is used to transfer the email to the concerned user. It works with web server.

When the user send the email through web server, it is delivered to the server that have SMTP protocol. The server extract the information of the recipient from the email header and send it to the correct user,