IMAP Server (Internet Message Access Protocol) is a method of accessing electronic messages kept on a mail server. It allows you to manage your e-mail directly on the server in organized, customizable folders.
NOTE: When this Site Application is installed you will no longer be able to read your new e-mail using the POP3 mail server.
For installation instructions, please click here.
NOTE: Once you have installed IMAP Server, you will need to reconfigure any existing e-mail accounts in you e-mail client to use IMAP as the Incoming Mail Server.
E-mail clients can be configured to use either POP3 or IMAP to retrieve e-mail and in both cases use SMTP for sending. By default, every account has POP3 installed for the e-mail retrieval protocol. If you would prefer to use IMAP, you can install the IMAP Server site application. Continue reading to learn the differences between IMAP and POP3.
What are the Differences Between IMAP and POP3?
E-mail messages are sent to an e-mail server that stores received messages in the recipient's e-mail mailbox. The user later retrieves these messages with either a web browser (webmail client) or an e-mail client that uses either IMAP or POP3 to retrieve those messages. The major differences of IMAP and POP3 are how this e-mail is retrieved.
IMAP Retrieval Protocol
IMAP organizes and stores the e-mail in folders on the server. The e-mail is then accessed and displayed the same no matter which e-mail client you use (i.e. Outlook Express, Thunderbird, Webmail, etc.). Because all of the info is stored on the server, any modifications to the e-mail account (e.g. creating/deleting/renaming of folders or messages) will automatically be updated for all users accessing that e-mail account regardless of e-mail client or location. (see Figure 1).
(Figure 1: IMAP E-mail Access and Organization Flow)
POP3 Retrieval Protocol
POP3 stores all of the incoming mail in one central inbox on the server which is then generally downloaded and organized with an individual e-mail client. Because all of the organization and modifications are not stored on the server, any changes made to the e-mail account will only be reflected on the e-mail client that made the changes (see Figure 2).
(Figure 2: POP3 E-mail Access and Organization Flow)
What are the Advantages of IMAP?
There are many good reasons to install the IMAP Server, here are just a few:
Feature Rich Webmail Clients
Because IMAP stores all of it's information on the server, you can install a webmail client with all of the advanced features of regular e-mail clients. POP3 webmail clients have never been able to elegantly handle folders, address books, etc.
Connected and Disconnected Modes of Operation
When using POP3, clients typically connect to the e-mail server very briefly, only as long as it takes to download any new messages. When using IMAP, clients often stay connected as long as the user interface is active and download message content on demand. For users with many or large messages, this IMAP usage pattern can result in much faster response times.
Access to MIME Message Parts and Partial Fetch
Nearly all internet e-mail is transmitted in MIME format, allowing messages to have a tree structure where the leaf nodes are any of a variety of single part content types and the non-leaf nodes are any of a variety of multipart types. The IMAP protocol allows clients to separately retrieve any of the individual MIME parts and also to retrieve portions of either individual parts or the entire message. These mechanisms allow clients to retrieve the text portion of a message without retrieving attached files or to stream content as it is being fetched.
Message State Information
Through the use of flags defined in the IMAP protocol clients can keep track of message state, for example whether or not the message has been read, replied to, or deleted. These flags are stored on the server, so different clients accessing the same mailbox at different times can detect state changes made by other clients. POP3 provides no mechanism for clients to store such state information on the server so if a single user accesses a mailbox with two different POP3 clients state information, such as whether a message has been accessed, cannot be synchronized between the clients.
IMAP provides a mechanism for a client to ask the server to search for messages meeting a variety of criteria. This mechanism avoids requiring clients to download every message in the mailbox in order to perform these searches.
What are the Disadvantages of IMAP?
While IMAP has many advantages over POP3, there is one potential disadvantage to consider:
Disk Space Usage
Because IMAP stores all of your e-mail information on the server, this can potentially use alot of disk space (as e-mail storage counts against your account quota). Generally POP3 will download the e-mail off of the server to an e-mail client and organize it locally, thus freeing up space on the server. This is usually not a problem unless you receive many large attachments with your e-mails.
What Happens When IMAP Server Is Installed On My VPS?
When IMAP Server is installed on your VPS, all of the existing e-mail users will be converted to IMAP automatically, and all newly created e-mail users will be set to IMAP. The location where your e-mail is stored will be changed from the default POP3 location to a custom IMAP location on your account.
What Happens When IMAP Server Is Uninstalled From My VPS?
When IMAP Server is uninstalled from your VPS, all of the existing e-mail users will be converted back to POP3 automatically, and all newly created e-mail users will be set to POP3. The location of your e-mail storage will be changed back to the default POP3 location on your account. Any user created folders (and their contents) will be lost, only the main Inbox data will transfer back to your POP3 storage location.
Can I Use IMAP and POP3 On the Same VPS Account?
By default, once IMAP Server is installed on a VPS, POP3 will no longer work. It is possible for advanced users to manually configure their account to use both IMAP and POP3 on the same VPS, but we do not provide technical support for this.