I've checked so many articles, but can't find one for server to server email receiving. I want to write a program or some code just acts as an email receiver, not SMTP server or something else.
Let's suppose I have a domain named example.com, and a gmail user user@gmail.com sends me an email to admin@example.com, or a yahoo user user@yahoo.com sends me an email to test@example.com. Now, what do I do to receive this email? I prefer to write this code in Python or Perl.
Regards,
David
"reveive" is not a word. I'm really not sure if you mean "receive" or "retrieve". 
If you mean "receive" then you probably do want an SMTP server, despite your claim. An SMTP server running on a computer is responsible for listening for network requests from other SMTP servers that wish to deliver mail to that computer.
The SMTP server then, typically, deposits the mail in a directory where it can be read by the recipient. They can usually be configured (often in combination with tools such as Procmail) to do stuff to incoming email (such as pass it to a program for manipulation along the way, this allows you to avoid having to write a full blown SMTP server in order to capture some emails).
If, on the other hand,  you mean "retrieve", then you are probably looking to find a library that will let your program act as an IMAP or POP client. These protocols are used to allow remote access to a mailbox.
How to receive an email on server? Better using Python or Perl