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C# custom mail server: receive email through socket on local machine

I'm writing unit testing for email validation.
I'm trying to write a very simple POP3 email listener (using sockets) so the email can be sent to my local machine using something like test#hostnameofmymachine.
I tried to do something like this: https://msdn.microsoft.com/en-us/library/kb5kfec7%28v=vs.110%29.aspx
But I don't know on which port the email will be sent so I can't create a socket unless I know which port to listen to.
How can the SMTP server (which sends the message) can know on which port to send the email? (IMAP 143? 993?) (POP3 110? 995?) So I don't know on which port I must listen to.
How can the SMTP know whether the receiver is POP3 or IMAP? How can it know whether SSL is supported?
I'm quite sure I'm missing some important information regarding email protocol.

POP3 and IMAP do not receive email, they only allow access to stored emails.
You need to write an SMTP server, not a POP3 server.

I recommend you to use this repository, it contains in itself most of the services you may need and it is easy to configure.
In our case we use the services:
Postfix with SMTP.
Dovecot for POP3.
SpamAssassin with custom rules.
OpenDKIM
OpenDMARC
LetsEncrypt and self-signed certificates
Persistent data and state
CI/CD
Extension Delimiters (you+extension#example.com go to you#example.com)
Docker Mail Server
https://github.com/docker-mailserver/docker-mailserver

how to know the different status of sended email in c#

I am Creating an application in c# . I have to know how can I know the status of the sended email.The status May be.
4. Track sent emails to determine if they were:
4.1 delivered
4.2 opened
4.3 recipient opt-out
4.4 bounced (with the reason for the bounce)
4.5 time/date sent
4.6 which links in the email were clicked (and time/date they were clicked)
4.7 IP address, if user clicked any links in the email
Should I use Any API or Dll or something else.Please help .Any Help will be Appreciated.

If you program your application to send mail through a hosted SMTP server like http://www.sendgrid.com or http://www.ultrasmtp.com, you can access the delivery status of messages that you've sent.

There is no easy way to do what you want. Actually this status can be tracked by your SMTP server itself and if you are using some third-party SMTP server like GMail or any corporate server, I 'm afraid they won't give you access to those information without using a authenticated client.
From your C# program, if the SmtpClient.Send() method returns true, you can assume the mail has been delivered to the SMTP server. If in case, the delivary fails, you should receive a mail to the outbound mail ID's inbox. If you want to make outbound mails appear in your outbox, you should configure IMAP/POP3 configurations accordingly.
There is no API or DLL available in exact form you want, as far as I know. You can try some other way like tracking a hash or embedded image in the mail-body from your server. But these are not reliable way as most mordern Messaging services have counter-measures for this.

How to use C# to connect to Exchange Server via RPC Over HTTPs

We have application implemented in WinForm. Now Customer requests to add new feature - Mail Function. That one i have to connect to customer mail server (Exchange Server) to send marketing email. They are using RPC Over HTTPS with Outlook Client to connect to Exchange Server. They asked me to refer this link http://www.msexchange.org/tutorials/outlookrpchttp.html
That all I know. When they asked, I even don't know what is RPC Over HTTPS. But after I did searching on Internet I understand a bit now. I really need a code sample for this problem.
Please advise me.
Thank you all a lot.
Regards,

What are you using to send messages now?
If you are using the Outlook Object Model or Extended MAPI to send using an existing Outlook profile, there is nothing you need to do - that will all happen under the hood.

Application to access, read & delete mails in my webmail with C#

I have been able to send mails from my own domain successfully. My problem now is that I need to access the account and retrieve all the mails that I receive from postmaster and process the information in the mail.
How can I do this? I have been searching the web but could only find solutions involving third party libraries. .NET doesn't bring an inbuild class that helps with this?

First you need to understand what protocols does the Mail Server in question support.
You can find this by either reading the help that accompanies it or search in Google for that Mail Server. You may also need to set some settings on the server before you can start coding.
After you understood what protocols your server supports, use some of the following:
If you are using a POP3 server, you may fine the following article useful : A POP3 Client in C# .NET
If you are facing IMAP or Exchange server, you may want to the link that Billy Coover gave you: Read MS Exchange email in C#

What type of email server are you working with? If it's exchange, there are some options: Access exchange e-mail in C#

First you can try to dedect what protocols(IMAP/POP3) supported by remote server.
You can try imap_clinet_app.zip or pop3_client_app.zip applications from http://www.lumisoft.ee/lsWWW/download/downloads/Examples/ to connect your server.
If you can connect, then specified protocol supported.
Both application comes with full source code, so if can use IMAP or POP3, you can use that library in your project.

how to create a SMTP server

I have an application that run on server,
I want that my application could received mail in order to start some function.
I would like to know what should I need to do in order to have this capability?
Do I need to build SMTP server? if so, how should I do it?

You can try: http://www.lumisoft.ee/lsWWW/download/downloads/ .
There is SMTP server component what you can use to recieve emails.
Or alternatively there is SMTP server written in C#, you can write message filter for server.
In filter you can access incoming message and do what ever you want with it.
--- Yes also as others suggested will work ok too, you just run simple mail server and get emails by pop3 or imap. Pop3 and Imap components and example applications also included in same link.

You can use IIS6 to receive email and drop it into a specified folder. Your app can then pick up those emails and do whatever it needs to with them.

Active the SMTP service in IIS. It drops emails in the C:\inetpub\smtproot\drop folder IIRC.
Then you just need a Mime parser to read the EML files. I used the one in Lumisoft when I did the same thing.

You could use any Mailserver to receive the mail and have your application check the poxtbox every 1 minute to receive the mails.
When any mail arrived (or special subject as you need), you could execute your code.
For IMAP you could look at this Library

I have previously had some success using the Chilkat POP3 component to programmatically monitor a POP3 account for incoming mail.