Sembee Blog of Exchange MVP Simon Butler

Why You Shouldn't Enable the POP3 Server

This is another post in my series of articles on why you shouldn't use certain features in Exchange, even though they are there. As with the other articles, the article does NOT tell you how to enable the feature in question.

The other articles in this series are:

- why you shouldn't use the POP3 connector: http://blog.sembee.co.uk/archive/2006/09/25/28.aspx
- home grown versus commercial SSL certificates: http://blog.sembee.co.uk/archive/2006/03/05/9.aspx

For this article I am going to outline some of the reasons why you shouldn't enable the POP3 server on the Exchange server. This is different from the POP3 connector, which is used by Small Business Server to pull in email from an ISP. This is POP3 used to collect email from Exchange.

Why is POP3 enabled?

POP3 is not enabled by default and there are a number of reasons why it is enabled.

Some administrators enable it because that is all they know, and they want to use Outlook Express for email. This is familiar to them and their users.
Others enable it for remote access, because either they don't know about or cannot use RPC over HTTPS (aka Outlook Anywhere (Exchange 2007) or Outlook over the Internet (SBS)) http://www.amset.info/exchange/rpc-http.asp

It may also be enabled to allow other non Microsoft clients to access email.

However in most cases it is a request from a user, who may or may not be completely up front about why they want to use POP3. POP3 can be used/abused in so many ways that it is one of the reasons why the Exchange server admin should really think twice before enabling it.

Therefore the first thing an Exchange Server admin should do when they are asked to enable the feature is ask the question why. If the asker then goes coy, you know it may not be in the business' best interest to enable it.

Why Shouldn't You Enable the POP3 Server

There are any number of reasons why the POP3 server should not be enabled. These are the most common reasons why not:

  1. Username and Password Sent in the Clear.
    In the default configuration, POP3 sends the username and password across in the clear. That is a security risk. If you really do need to enable it, look at using SSL to secure it. 
  2. Risk of content loss.
    POP3 is designed to REMOVE the content from the server and store it locally. It is too easy for a user to download the content and remove it from their mailbox. While there is a setting to leave the email on the server, it cannot be controlled server side, so you are reliant on the user setting the client in the correct way.
    As the data is being stored locally, it cannot be backed up easily, therefore if the user loses their machine, it is stolen or suffers a hardware failure, then the email is lost as well.
    I have also seen it abused, as a way to get content out of the network - sales people in particular want the feature so they can store a copy of everything at home. A significant number of sales people are not loyal to their employer at all, and would prefer that their clients do everything through them, ideally on a personal email address.
  3. Loss of control of access.
    Once POP3 is enabled, it can be used by any number of things, PDAs, phones, Blackberry etc. The IT department may or may not know about those, and be unaware of them in the event that they cause a problem. 
  4. Storage and Regulatory Compliance Concerns.
    If you operate in an environment where you have to store email or be aware of the content of the messages, then that is a big argument not to enable POP3.
    If the client is configured for POP3 and email is sent from that client, then there is no way it can get back in the store unless it is imported. If the user is sending email with something obscure, then that isn't going to happen.
    The user could also be sending email out through another SMTP server, even sending email with their personal email address as the reply to address (again sales type people are notorious for doing this - then claiming it was an "accident").
  5. Feature Loss
    You also lose the GAL, calendaring and everything else that Exchange offers. If the email is being extracted then OWA becomes close to useless, no sync to Windows Mobile devices over the air.

If your must enable the POP3 Server

As with many things in the Microsoft world, everything is enabled until you turn it off. POP3 access is no exception. If you enable the server then all users will be able to use POP3. Even if you don't publish the information about how to configure it, if OWA is used and the port is open, the users will soon work it out - the information is all over the internet.

Therefore if you must enable it then you should secure it.

  1. Use admodify.net to disable the feature in bulk for Exchange 2003 users, Exchange Management Shell for Exchange 2007 users. Then enable it for the users who need it only.
  2. Use SSL and only open the POP3S port (995). That will slow down a causal user.
  3. If you can, use IMAP instead. That leaves the content on the server. It isn't perfect as there is still the chance that email is sent out via another SMTP server, but it is better than POP3.

Conclusion

Make sure that management are aware that it is being enabled and are aware of the risks that are involved. If they say no (which is ideal) then you can simply turn down future requests with that same message.

My personal opinion is that POP3 has no place in a corporate email environment and there is no need to enable it at all.
If you need to provide access to mobile devices, then purchase suitable devices that use either Windows Mobile or Blackberry.
If you need to provide access to non-Microsoft clients, use IMAP.
If you need to provide remote access for Outlook, then use RPC over HTTPS.

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