SMTP question - a session containing multiple transactions

[Joe Hwang <joedothwang@xxxxxxxxx>]

I am a newbie. Could anyone clarify about the following issue?

I am aware that once a session for SMTP is established it could be used for multiple transactions. 

Let's say that there are two SMTP servers, A and B, and A initiates a session (TCP connect to B). After A finished one transaction (transferring some email content from A to B), is it possible B starts transferring some email content to A using the same TCP connect? What is the command or process like? Can B just use "mail from" after A sending its emails to B?

Thanks,

Joe.