SMTP Question.

[azfarhashmi]

I have a query about SMTP. At the movement I am thinking that SMTP is only required to send mail from client to server or server to server. but some one told me that SMTP is also required when I send a mail e.g From: azfar@hotmail.com To: azfar@yahoo.com
In this case he told me that at yahoo.com SMTP is responssible to recieve mail from hotmail.com too then client can see this mail via POP.
So I wanna know who is responsible for recieve mail at server level. If I install a mail server for azfar.com and add its MX record to DNS and then stop my SMTP service then can my server recieve mails from other or not.

[Tuttle]

In general, POP and IMAP are only useful for receiving mail from a mailbox server, ie once it's completed its journey. Getting it there, both from the client to the client's local server and then to the recipient's server, requires SMTP.

If you want to receive mail for a domain on a server, it must be running an SMTP service.

[azfarhashmi]

But I am still in doubt you told me that to send a mail from server A to server B, server A must running SMTP but what about server B to recieve does it also require SMTP service running or not. If not req then who is responsible for recieve mail on server B. And if SMTP is respobsible for both then what is the function of MTA.

[Tuttle]

SMTP is a protocol. For two machines to exchange a message using SMTP, both devices must be running software that speaks SMTP. SMTP is used for the initial submission (sending PC to mail server) and for the communications between servers.

MTA is a term defined in the SMTP protocol, and it stands for 'mail transfer agent' -- it's basically a mail server. MUAs (mail user agents) are end-user email clients.

A typical email path looks like this: SMTP SMTP POP/IMAP
PC A ------> Server A ------> Server B ----------> PC B
MUA MTA MTA MUA PC A (acting as an SMTP client) sends the message to Server A (SMTP server) using SMTP.
Server A (SMTP client) sends the message to Server B (SMTP server) using SMTP.
PC B (POP/IMAP client) retrieves the message from Server B (POP/IMAP server) using POP3 or IMAP4.The two PCs are running email clients, which support at least SMTP and one of POP3 or IMAP4.
Both servers need to be running SMTP services. That allows mail to be both sent and received using SMTP.
Server B is also running a POP3 or IMAP4 service so that PC B can check the mailbox.