Email works in following ways:

1. Message is created: It can be created by a user using Mail User Agent (MUA) or a software or notification system.
2. Message is delivered to MTA (Mail transfer agent) : MTA get message by two methods:
a. Simple Mail Transfer Protocol : It is an internet protocol (25) for transmission of messages. I have I think in one of my thread had explained how.
b. Local Interprocess Comunications (IPC) : They are use for transferring message between softwares. :
3.MTA forward it to MDA ( Mail Delivery Agent) : There are two MDA:
a. Local MDAs: For transferring message in the
same server.
b. Remote : They are use for delivering over
the net.
4.Local MDA / Remote MDA to Local MDA : Again mail is tranferred to Local
MDA.
5.Acessing of email by user : Atlast mail is access by users
using POP3 with help of
applications like outlook , Thunderbird , or evolution using IMA via browser.