Email Works Like This Email is Similar to the Post Office
In the world of snail mail, the sender writes a letter and drops it into a mail box. When this happens, the letter has just entered a sorting and transportation system where it stays for some amount of time. Eventually the letter ends up with a mail carrier who delivers it into the mail box of the receiver. The receiver opens the mail and, ah, lets it lay on the front hall table until someone throws it away. To find the mail later, the receiver must dig through the trash. If the receiver needs the mail while away from home and the trash, well, too bad.
Email works somewhat similarly to this:
- A person creates and sends an email using client software called the Mail User Agent or MUA. Outlook, Eudora and Mail are MUA’s. Creating and sending email is similar to writing a letter and dropping it into a mail box.
- An email server, known as a Mail Transport Agent (MTA) routes the message across the Internet to another MTA. This is analogous to sorting and transporting snail mail.
- The receiver of the email contacts the MTA or email server using another client (MUA) and reads the email. This is like the mail carrier delivering a letter and the recipient opening and reading it.
So email uses three basic types of software, running on client and server hardware:
Mail User Agent Running on the users’ machines, the MUA — or client software — enables the creating, sending and receiving of emails from the desktop.
Mail Transport Agent The MTA runs on a server. An email typically goes through two MTA’s – one local to the sender and the other local to the receiver – when sent from one email client (MUA) to another. The most popular MTA software on the Internet is SMTP or Simple Mail Transfer Protocol.
Mail Delivery Agent The MDA is also known as the POP server or IMAP server or both. It can also be a webmail server. This software often runs on a server, normally along with the MTA. It is local to the recipient’s MTA and delivers email to local mailboxes for the MUA.
POP and IMAP MDAs
There are two primary types of Mail Delivery Agent software: POP and IMAP. Both POP and IMAP are industry-standards and the dominate means of people receiving their email.
POP The Post Office Protocol is the oldest widely used Internet Mail Delivery Agent. Its current implementation is POP3. POP is a simple protocol to configure, operate and maintain. When using POP, a client goes online with the email server, downloads the mail, then goes offline.
POP messages are stored on the mail server until downloaded to the client software on the user’s machine. The messages are then stored on the client machine and deleted from the server. In recent years POP has added the option to leave email on the server after downloading it. This enables a user to download the same mail using multiple POP clients on multiple computers. Each email client can download the same messages one time.
IMAP The Internet Message Access Protocol is a more recent development in email technology. Its current implementation is IMAP4. IMAP can do all of the POP functions, plus many more. It can be simple or complex to configure, operate and maintain. IMAP was designed for users to stay connected to one or more email servers while reading, creating and organizing messages.
Users can manipulate both mail and mailboxes on the IMAP server where the mail resides. Server-side mailboxes can be added, nested, renamed, moved and deleted. Mailboxes can be for private and shared access. Shared mailboxes are available for such uses as mailing lists, announcements and common projects. Messages can be freely copied and moved between mailboxes on multiple accounts on multiple servers. Mail can also be cached on the user’s machine for offline reading. Unless prevented through security measures, the user can view mail using any IMAP client or any client machine.
MDaemon supports POP email in its standard version. It supports both POP and IMAP in its Pro version.
In addition to sending and receiving email, MDaemon can scan email for viruses and spam. It can also host mail lists and catalogs. These are functions discussed in other howtos and whitepapers