Sunday, May 31, 2009

The difference between POP and IMAP

There are two basic ways to set up an email program such as Eudora, Entourage or Outlook to check your email. One is to use a POP (POP3 actually: Post Office Protocol) and the other is to use IMAP (IMAP4 actually: Internet Message Access Protocol). POP is the most common way of doing this but from our point of view IMAP has certain major advantages over POP and that hopefully will become clear to you in a minute. Please don't confuse IMAP with IMP - IMP stands for Internet Messaging Program, and it's the web application used to read your NYUMC/Skirball email from a web browser, better referred to as webmail. There is a certain relation between IMP and IMAP but they're entirely different animals and the similarity of the acronyms is incidental.

If POP is used all your email messages are downloaded from the email server to your computer and stored on the hard drive. Most programs have the option to keep the messages on the server for x number of days but sooner or later the messages are removed from the server. Also, with POP your outgoing emails are kept locally on your hard drive which leads to the familiar and annoying situation where you have different emails on each computer that you use to check email: home, office, work, etc. Furthermore, the local file used by your email program to store messages is specific to the program, there is no widely accepted standard. So, if you ever decide to switch your email program, you will find it necessary to export/import the emails from one program to another which is often painfully slow or doesn't work very well at all. In some cases when moving between different programs and different operating systems (Mac, Windows, Linux) it may be altogether impossible. Most people don't even know where these files are and don't make any backups and don't know how to move them to another computer. POP has basically only two advantages: once the emails are downloaded to your computer, they open very fast since they reside on your local hard drive and your mail storage capacity is only limited by the free space on your hard drive, it's not subject to quotas and size limitations imposed by your mail provider, be it NYU, Earthlink, Verizon, etc. Also, POP is easier to implement and support and it creates less network traffic for your internet provider. For these reasons POP is often the only way your ISP will support.

If IMAP is used all your email messages are stored on the server and never removed. In most cases your email application creates a local cache of messages on your hard drive to speed up the opening of emails, but the originals are not touched. Also, with IMAP (this is the big one!) your sent mail and drafts are uploaded to the server! Because of this, you will see the same incoming and sent messages from any computer as long as your mail program is configured for IMAP. POP3 does not have this functionality. Furthermore, the IMAP folders on saturn are the same ones that IMP (the webmail program) uses. Therefore, if you use IMP to send email while being away from the Institute, then come back to your office, open Entourage you will see that email in your sent mail folder! Or, if you save your message-in-progress in the office it'll get uploaded to your drafts IMAP folder and you will be able to open it at home and continue working on it. Pretty neat, isn't it? Of course like anything good in this world it comes at a price:( First, reading email over IMAP is slower because messages are read "live" off the mail server. It's particularly slow the first time you open a folder or a message as it has to be downloaded and cached. Each next time it's quicker though. But IMAP is inherently slower than POP3, in particular over slower connections. The other negative side of IMAP is that it's sensitive to the size of your mailboxes, at least this is the case with certain mail servers as the one run by us. That is, if you have a lot of messages in your inbox checking your email may become slower and slower over time as your inbox grows large. Also, if your email provider imposes quotas IMAP may become a problem. To address this you need to manage and archive your email. You can create additional IMAP folders and move emails out of your inbox and sent mail. In most cases it's enough to do this once a month. On Saturn we don't impose email quotas though. Your mail storage is limited only by free space in your home directory, but you still need to manage your email to avoid the slowdowns, this is a technical issue.

Since IMAP is an internet standard and the emails are stored on the server it's easy to switch between email programs and operating systems. You can move or setup additional IMAP accounts in Outlook XP under Windows and Mail.app in OSX or Thunderbird uner Linux with equal ease and within minutes you will see all your emails even if you don't have access to your previous program or the other computer. There is no need to copy any files between computers just configure a few settings.

Also, with IMAP we can enable automatic spam filtering for you and the IMAP mail is backed up nightly.
Here is more info on spam filtering on Saturn.

As far as functionality and convenience are considered IMAP is the way to and we encourage you to switch to IMAP. We're working on a page with instructions and we're here to help you with the conversion as well.

Not all email programs have IMAP implemented properly though. All versions of Eudora are notorious for not being able to upload sent mail to the IMAP server properly, therefore we do not support IMAP under Eudora! Our preferred email program is Entourage and we support it 100%. It's a commercial program that comes as part of Microsoft Office for MacOS. We also support IMAP under Mozilla Thunderbird and the latest versions of Apple Mail that comes with OSX 10.4 (Tiger).

If you start using IMAP you should no longer use POP on any other computer! Using a mix of POP and IMAP will lead to conflicts and will basically defy the purpose of switching to IMAP in the first place. To get the the full benefits of IMAP you must switch to IMAP exclusively. For the reasons mentioned above it's OK to continue to use webmail (IMP) as it is essentially an IMAP client.

SUMMARY

POP advantages

- messages load very quickly once they're downloaded
- messages are stored on your hard drive so they're not subject to server storage limits and quotas
- widely supported by ISPs and email providers
- all email programs support it

POP disadvantages

- messages are stored on your hard drive so they're not accessible from other computers
- sent mail and drafts are not accessible from other computers either
- messages are eventually removed from the server
- messages are stored in files that are not compatible between different programs
- it's usually difficult to migrate from one program to another, sometimes impossible
- it's cumbersome to copy your email to another computer (office, home, school, laptop, etc.)
- users normally don't have backups of their email

IMAP advantages

- messages are stored on the server are accessible from any computer and webmail anywhere in the world
- IMAP mail folders remain synchronized with IMP (webmail)
- sent messages and drafts are also stored on the server
- server-side spam filtering is easily implemented with IMAP
- IMAP mail is backed up nightly on the server and can be restored
- ease of migration from a program to a program and from a computer to another computer/location
- ease of setting up additional computers to check your email, no need to copy anything fro one computer to another

IMAP disadvantages

- messages load slower, in particular the first time they're read
- sensitive to size and requires periodic archival of email messages
- subject to storage quotas (not the case with Saturn, however)
- very few ISPs and email providers offer IMAP as it is considered a high end option and it's complex for them to support
- not all email programs support it properly

Saturday, May 16, 2009