Understanding Email Protocols (POP, Imap, MAPI, EAS, Exchange)
The email protocol is the process by which an email desktop/mobile client accesses the information (From and To) contained in an email account (your email address). Each of these protocols which are governed by universal standards (at the core level) have a specific set of capabilities in terms of how data is handled at the server level and stored at the local level. This article doesn’t focus on the “how-to configure” aspects of a given protocol. That will be covered in greated detail in “Understanding Outlook Configuration & Profiles”. The purpose here is to provide an understand of what happens with each of the main protocol in use today.
The information regarding how an existing email account is configured in the Outlook profile is found by looking at the accounts configured under <Account Settings –> Email tab). This can be reached in one of two ways, directly from within Outlook by going to
(in Outlook ‘2010/’2013’2016)
File –> Account Settings –> Email tab
(in Outlook ‘2007)
from menu bar –> Tools –> Account Settings –> Email tab
(using the Control Panel <Mail> app)
click on <email accounts>
the result for any of the above will be similar to the following
Protocol support – email client versus email server
What protocols are supported by a given email desktop/mobile client depends solely on the developers of the given client. It has nothing to do with what is or is not supported at the server level. For example, Thunderbird cannot support Outlook.com using the EAS protocol and it can’t access a Microsoft Exchange account natively without an addin. Thunderbird could access an Exchange account via either the Imap or POP protocols but that is different then accessing the server using the native Exchange protocol.
By the same token, not every email service provider supports every emai protocol. With the exception of Outlook.com and hosted Exchange accounts, generally, only POP3 and IMAP are supported by a given provider.
In terms of contact/calendar data, neither the POP3 or IMAP protocol supports these data items. In Outlook (desktop), 3rd party addins are required to access such things as Google or iCloud based contact/calendar items. In the case of Google, this would required the Google App Sync addin (provided by Google with paid Google accounts). Apple provides an Outlook addin to connect to iCloud data. There are also 3rd party programs available that provide a wide-range of extended features such as Sync2 from 4Team or CompanionLink for Outlook from the CompanionLink folks.
The email clients on some devices are able to directly connect to contact/calendar info from various providers such as Google, Yahoo etc. This is done via extensions to the email client no different then installing an Outlook addin to accomplish the same thing when using Outlook (desktop).
Summary of email protocols
POP3 (Post Office Protocol 3)
This protocol allows for a “one-way” movement when reading email from the server and then stored in a local data file. In the case of Outlook – POP3 accounts utilize .PST files for POP3 accounts whereas Thunderbird uses .mbox files. How information is stored locally is governed by the email client and the ability to move information from one program to another depends solely on the import/export capabilities of the email client. Outlook for instance cannot import data from .mbox files and Thunderbird cannot directly import data from a .pst file without a version of Outlook being installed.
POP3 only involves new email that has arrived in the <Inbox> on the server hosting your account. It does not support any kind of sub-folder structure at the server level and similarly has no functionality in relation to such things as contacts, calendar and tasks.
With POP3, there is one very important setting that governs what happens at the server level once the desktop client has read any new email that has arrived which is whether or not the newly arrived email should be left on the server after it has been downloaded to your desktop client or leave a copy of it on the server and it’s really important to understand the ramifications of the choice once made especially if you have limited <Inbox> space on the server. The additional option available at the server level is to indicate a time period (i.e. 14 days) after which anything on ther server reaching that age AND has been read, gets deleted from the server.
This setting is found in the <More Settings –> <Advanced> tab when configuring a POP3 account
The other notble item related to POP3 accounts is that this is the only protocol in Outlook that enables multiple POP3 account to use a single PST data file for the delivery of email. This can be done at the time the email account is configured using Outlook ‘2010 or later or can be done after the fact at any time in any version of Outlook (Outlook ‘2007 and earlier requires that this be done after the account is configured). All other protocols will result in a separate data file being created (see Understanding Outlook PST and OST Data Files for additional information)
In Outlook ‘2010 or later, it’s important to take note of the option when it presents itself as shown below
Doing this after the fact requires going into <Account Settings –> Email tab –> highlighting the POP3 email account –> changing the delivery location as shown below
Note: the pst file must already exist in the profile. If it doesn’t, it must first be added.
Some POP3 limitations:
- Deleting an individual item does not remove it from the server
- If mail is left on the server, care should be taken that there is sufficient capacity allowed before senders encounter a bouce-back message being informed that the “mailbox is full – try again later”. Each ESP sets its own rules of how much email can be stored for each account.
- Sending an email which ultimately gets saved in “Sent Items” folder is available locally only – not on the server. That means that any messages sent via Device #1 will not be accessible via Device #2.
- Contacts, calendar, tasks are local to the specific machine. Those items are not stored on the server regardless of what capabilities exist with your WebMail interface
IMAP – (Internet Message Access Protocol)
This protocol allows for the two-way movement of email items between desktop/mobile allowing for the creation of additional mail folders. In essence, when an account is configured as Imap, the desktop client connects to the server and synchronizes the contents on the server with the locally stored data. Unlike a POP3 account, additional folders are supported including the <Sent Items> folder, items deleted locally will get removed from the server and vice versa. Like a POP3 account, this protocol does not support anything related to contacts, calendar and tasks which is information stored locally when created by the email client or only on the server if created via Webmail.
Not all Imap servers and ESPs are the same but, for the most part, are reasonably consistent across the board. The base folder structure in an Imap account depends on how the server constucts the initial folders. For example, a Gmail Imap account maintains a number of folders such as <Drafts> <Sent Mail> <Trash> etc under a root folder called <Gmail> whereas an Imap email account with another ESP has a single root for all its supported folders using different names like <Sent> instead of <Sent Mail> or <Deleted> instead of <Trash>. The base folder structure is governed by the server, not the desktop/mobile client.
In essence, the locally stored data for an Imap account is a mirror of what is contained on the server providing that the email client has been set to “subscribe” to a given email folder located on the server. A server can contain a 100 different custom email folders beyond the typical <Inbox> for use by different individuals so each person may only want to “subscribe” to the individual folders that are of interest.
Every IMAP account will have its own data file with its own <Inbox> and email folders. In Outlook ‘2010 and earlier, there will be two PST files created (if this is the first account configured in the profile). The first will contain the email folders and the other named “Outlook Data File” by default will contain the default contact/calendar folders for the profile. The a new <email related> PST file will be craated any time the IMAP account is configured. Starting with Outlook ‘2013/’2016, an .ost data file is used which will contain contact/calendar folders with the added description of “This Computer Only”. It is really important that the significane of “This Computer Only” folders is understood otherwise you run the risk of unexpectedly losing this data. Additional info can be found in How to Protect Outlook ‘2013/’2016 Imap Contact/Calendar Data
Major Imap Advantage
Allows for viewing and use of the same email contents across multiple devices at all times. Items deleted in Device #1 will be reflected on all other devices and messages sent from any device will also end up being accessible by the other devices.
Imap consideration/limitations
- Like POP3 – must ensure that your ESP provides you with sufficient capacity to store all your email items that you want to maintain on the server over time.
- Like POP3 – contacts, calendar and tasks etc are not handled by the Imap protocol. This information is either stored locally when created by the email client or on the server via the Webmail interface.
MAPI – (Messaging Application Program Interface)
There are two primary versions of the MAPI interface known as “Simple MAPI” (the protocol used by Outlook Express on Win ‘XP) and “Extended MAPI” as employed by the Outlook Hotmail Connector for Outlook versions up to ‘2010 connecting to an Outlook.com (Hotmail) account that has not yet been migrated to the Office 365 backend Exchange servers.
The Outlook Hotmail Connector (and MAPI protocol) are no longer applicable once the account has been migrated at which point the account will need to be re-added to the Outlook profile by entering the email address/password. Outlook will then configure the account using the <Exchange> protocol and the Outlook Hotmail connector should be removed from the profile if there are no other <non-migrated> Outlook.com accounts involved.
Note: Any Outlook.com account can also be manually configured as a POP3 or IMAP account in which case the Outlook Hotmail Connector does not apply.
EAS – (Exchange ActiveSync)
The EAS protocol began life as the mobile protocol used to synchronize with Exchange servers and then being made available (for a fee) to mobile vendors to standardize the way to connect with Outlook.com (formerly Hotmail). EAS was then incorporated directly into Outlook ‘2013 to connect directly with an Outlook.com account eliminating the need for also having to install the Outlook Hotmail Connector previously required in earlier versions of Outlook.
Like MAPI, it supports synchroization of contacts, calendar and tasks but does not support sync’ing of things like notes and drafts. A major misunderstood sore-point is the lack of ability to sync Contact Groups created via the Outlook.com web interface to Outlook Contact Groups since the two employ radically different approaches. This is a limitation of the EAS protocol itself (at the time of writing). Outlook.com “Contact Groups” are created with the use of “categories” whereas Contact Groups created in Outlook (the desktop client) are created as special contact item types with a specific MessageClass (IPM.DistList) making it compatible with all earlier versions of Outlook using the MAPI interface via the Hotmail Outlook Connector. In short, you cannot synchornize Contact Groups using an EAS Outlook.com account and Outlook ‘2013.
The limitation related to Contact Groups (along with a number of other issues) disappears once the Outlook.com has been migrated. It should be noted that Outlook.com accounts originally configured using the Exchange ActiveSync protocol will continue to work normally after the account has been migrated on the server side. The account will need to be readded to the profile and Outlook will automatically use the <Exchange? protocol and re-sync all the data. The old Outlook.com can then be reomved. To determine if your Outlook.com account has been migrated, log ito the account using your browser and if it shows anything other than <Outlook.com> (i.e. Outlook Mail or Outlook EMail), the account has been moved to the new platform.
Exchange server accounts (local)
Local exchange servers are used by organizations to host, manage and administer their own email. Information regarding a local Exchange server account applicable to an individual have to be supplied by the Exchange administrator in the organization responsible for the Exchange server(s). Outlook connects to any Exchange account via the Extended Mapi Exchange protocol. Outlook ‘2016 no longer supports Exchange Server ‘2007 and can only configure an Exchange using <auto-discover> which must be properly configured by the organization’s Exchange admin.
Exchange server accounts (hosted)
An alternative to an organization managing their own Exchange email servers is using a Hosted Exchange Provider available either directly from Microsoft or any number of 3rd party Hosted Exchange providers. Individuals or small business groups can also take advantage of an Exchange environment by either subscribing to a Microsoft Exchange account on a monthly per user basis or one of the various Office 365 Business subscription options (a starting point for comparing options can be found at https://office.microsoft.com/en-ca/compare-office-365-for-business-plans-FX102918419.aspx)
SMTP – (Simple Mail Transport Protocol)
There are two components to a complete email protocol, the one used to <retrieve> new email (incoming/inbound server) and the other used to <send> new email (outgoing/outbound server). SMTP is the protocol used to <send> new mail regardless of what protocol is used to <retrieve> new email which is why POP3 and Imap accounts are shown as POP3/SMTP and Imap/SMTP account types in the Outlook account settings. All external internet email is sent using the SMTP protocol from an SMTP server. Even Exchange servers employ an SMTP service when sending out messages outside of the organization.
iCloud – (Apple’s email account interface)
iCloud is used on Apple devices to synchronize its devices to an Apple email account supporting all the various item types like email, contacts etc. It is essentialy an Imap interface for email with extensions for contacts, calendar etc.
Accessing an iCloud account using Microsoft Outlook is done via an Outlook addin provided/developed/supported by Apple. There is no native functionally in Outlook to access an iCloud account any more then there is using an Android mobile device. How Outlook interacts with an iCloud account is governed by the Apple addin which typically must be upgraded with each new version of Outlook. Apple is the primary vendor responsible for support for all issues related to the iCloud addin.
There are alternative 3rd party approaches to using the iCloud addin such as Sync2 or CompanionLink for iPhone.
Category: Understanding Outlook
