Written by Daniel Fletcher Category: eMail
Published on 07 October 2011


Email has become a widely means of communication, certainly indispensable in business.  It has evolved over the years and presently there are a number of email systems available.  To choose the right one and troubleshoot when problems arise, one needs a fundamental understanding of how they work.


Email delivery is analogous to the post office system.  Email originates from a sender, who must deliver it to a post office (a mail server).  Once in the post office, it is up to the postal system to figure out where the message is to be delivered.  Once it arrives at the post office responsible for a mailbox, the message is delivered into the mailbox.  It is up to the recipient to go to that post office to retrieve the messages stored in the mailbox. Thus, there are two underlying functions: getting email to and from the post office, and the post office itself that manages the task of receiving the messages and transporting to the destination.

The Post Office

The method/protocol used to send mail to a server, or from server to server is called SMTP (Simple Mail Transfer Protocol).  SMTP defines the method of addressing (the envelope), but does not care about the content.  The post office consists of servers that receive the mail from users, then process the mail, figure out where it should be delivered, and finally place it into the recipient’s mailbox.  The processing part can take a number of steps.  For example, the server receives a single message, regardless of the number of recipients.  The server needs to determine how many recipients are listed for each message and generate one copy for each recipient, then determine which server or servers handle the mail for each of the recipients and pass on the message(s).  Often there are multiple servers involved, where one server or bank of servers are designated to receiving incoming mail, then pass the message on to other servers dedicated to sending the messages out.  Other times, intermediary servers process the messages and strip out viruses and spam first before routing the messages on.  The list of servers that touched each message can be viewed in the message header.

The User Experience

To retrieve messages from the mailbox, several methods/protocols are available.  The following are the most widely used types of email retrieval methods (in no particular order):

1. POP3


3. Webmail

4. Gmail

5. MicroSoft Exchange

6. Mobile

7. Unified Messaging


POP is an acronym for Post Office Protocol.  POP was one of the original methods of retrieving email from one’s mailbox and is perhaps the most widely used.  It provides a means of retrieving messages from the mailbox on the server and download them to the local computer as a batch, one by one.  The messages are then typically stored on the local computer and removed from the mailbox on the server.  This type of email is usually used with an email client program, such as Outlook, Thunderbird, or Eudora, among others.


- Provides quick access to one’s mailbox

- Email is downloaded to the local computer, allowing full control over storage and organization of the messages

- Increases privacy by not keeping all email at a server out in internet land, subject to hacking

- Promotes offline access to all previously retrieved messages, reducing the load on servers


- Generally, once email had been retrieved, the messages must be accessed on that machine only.  This limitation can be overcome by combining additional services.


IMAP is an acronym for Internet Message Access Protocol.  The latest version is IMAP4. This protocol provides an interactive means of manipulating messages stored at the mail server using a client program.   The actual messages are stored in the inbox at the home server.  One can view and delete messages from the inbox, and leave the rest there.  Messages are typically not downloaded to the local computer, but rather are left there on the server.


- Provides a means of accessing a mailbox from more than one device while seeing the same contents from each device


- All mail is left on the server, making it susceptible to being read by third parties

- The mailbox may become full, causing additional messages to be returned to the sender

- Less control over the organization of messages


Webmail is essentially an interactive middleman that provides access to a mailbox on the server, but using a web browser.  All email is kept at the home server and not downloaded to the local computer.  Webmail is not a protocol in itself, but rather an interface that typically uses either the POP or IMAP protocols to access the mailbox in the background and present the mailbox contents to the user.  Popular webmail access services include Hotmail and Gmail, although a lot of service providers now also provide a webmail interface for their users, using such interfaces as Squirrelmail, Horde, etc.


- Provides access to one’s mailbox from any PC with internet access and a web browser


- Webmail from service providers is stored “out there” and subject to hacking and reading by third parties

- Most webmail service providers are US based and as such are subject by the Patriot Act to hand over all mailbox content to the “authorities”

- Most webmail service providers sustain their business operation by embedding/showing advertising along with the mailbox contents.  Gmail’s advertising is further targeted by an automated process that “reads” the message content.



Gmail is an email service provided by Google.  It is listed here as a separate category because it provides a variety of methods of access to a mailbox through a combination of paid and free services.  The free service provides a standard webmail access to a mailbox that must be in the domain of gmail.com.  The service is sustained by advertising shown on the user interface.  Additionally, they also provide both POP and IMAP access to mailboxes.

A separate offering from Google/Gmail is a paid hosting of mailboxes.  Through this service, one can have a full domain of one’s choosing (ie: This e-mail address is being protected from spambots. You need JavaScript enabled to view it. ).  The cost is between $3 to $5 per mailbox per month.  Through this service, users can still access the mailbox through their webmail access, through POP, IMAP, through a Gmail app designed for Blackberry phones, through any of the popular email client programs, or through a plugin that works with Microsoft Outlook.  These mailboxes currently have a limit of 25 Giga Bytes.


- Provides convenient access to one’s mailbox from any web browser

- Google performs some junk mail filtering

- The paid service also provides seamless integration for users of Outlook that allows synchronized access between the local and web copy of email, contacts, calendar, and notes.  Additionally, shared calendars, company announcement pages can be set up.

- The paid version eliminates the need to perform additional backups of the email data.


- Gmail outages

- Email is being stored “out there” subject to hacking

- Cost for the paid version

- The plugin to automatically sync is available currently for the Windows version of Microsoft Outlook, but not OS/X or Unix/Linux

Microsoft Exchange

Microsoft Exchange is an email server product that provides a significant amount of functionality beyond just email.  It starts with a full email server capable of operating as a full post office for receiving and forwarding email through the SMTP protocol.  It also provides full POP and IMAP protocols for retrieving email using the typical email clients.  There is also a complete web access service.  Exchange can scale to enterprise organizations with tens of thousands of mailboxes spread across multiple physical locations.

Beyond email, Exchange was really designed to work with Microsoft Outlook.  Outlook integrates fully with Exchange and provides company-wide integration of mailboxes, calendars, to-do lists, notes, contacts, and address lists, shared document libraries, and automatic server-level message routing.  Complete security control is provided to allow users their data and designate who has access to what and what type of access (ie: read-only v/s modify).


- Provides a comprehensive solution

- Excellent web client allowing comprehensive access to most functions from any PC with an internet connection and web browser


- Complex to deploy and manage

- Cost prohibitive to run in a reliable fashion in installations of 50 or less mailboxes because it should run on a dedicated box plus the cost of the Windows server, Exchange server, and client access licenses

- The web interface is inconsistent and some functionality lost in non Internet Explorer browsers


With the proliferation of smart phones, mobile access to email has become widespread.  There are several methods employed, and are dependent on the capability of the phone, the phone service company, as well as the data plan subscription.  Many smart phones provide an email client that functions as either a POP, or IMAP client.  This is often referred to as “pull type” of email, because one has to tell the phone to check the mailbox.  Some phone companies provide a “push type” of email, in which their systems poll the server where the mailbox is hosted, and forward any new messages onto their client’s phone.

Android powered phones generally provide an email client with POP and IMAP access, and client applications are also available to connect to MicroSoft Exchange servers.

In addition to POP and IMAP access (both push and pull, depending on the phone company), Blackberry phones provide the Blackberry Enterprise Service (BES) when coupled with the correct data access plan and server.  The BES provides a complete, mobile solution that provides wireless synchronization to the email box, contacts, calendar, memo, and notes.  It does, however require a Blackberry Enterprise Server and MicroSoft Exchange server in the back end to communicate with.  A significant advantage for business users is that all wireless communication between the Blackberry and the BES are fully encrypted.  Alternatively, there are third party solution providers that provide this service for a monthly fee, thus eliminating the need for in-house servers.

Apple’s iPhone also provides POP and IMAP access.  It also has Blackberry Enterprise Service integration (see above) and Exchange Active Sync that provides full wireless synchronization with Microsoft Exchange.

Windows Mobile powered phones provide Exchange ActiveSync wireless push synchronization with Microsoft Exchange servers, thus providing the functionality similar to Outlook, but in a mobile phone.

Unified Messaging

Unified messaging is an emerging application of email in which the email system is used as a transport to send various types of communication.  Email started out as simple text.  We have seen email content and presentation improve over the last few years with the proliferation of email client software that supports html for formatting.  This allows specifying font types and sizes, embedding graphics, etc.  Unified messaging takes this a step further by allowing items such as faxes, scanned documents, documents, graphics, voice messages, and video to all be integrated and send through the email system.  This allows, for example voicemail and video messages to be viewed or played back and sent through the computer, instead os disparate systems.


I hope this gives you a good understanding of the various underlying technologies used in email communications.  Whether a plain text message or a rich video message sent from a mobile phone, email now allows us almost instant communication regardless of distances.  There is no single method suitable for all uses.  By having an idea of the features and limitation of each technology, one can then better decide the most appropriate technology for the task.  This article about how to choose an email service will help further examine the application and decide the best type of service.



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