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TechRepublic Tutorial: Limit mail size on Exchange to improve security and speed

How and why to limit mail size in Exchange


By Dean Lorenson

There are several advantages to imposing a limit on incoming and outgoing Internet messages. There are also several disadvantages. In my experience, the advantages far outweigh the disadvantages.

I have a limit of three megabytes on my organization’s Internet Mail Server. This means a user can’t send or receive messages that are larger than this. If they attempt to send one, the message is returned with a Non-Delivery Report telling them that the message has exceeded the limit. If a message is sent from outside the organization, a similar message is sent to the originator. Obviously, this puts the user at a disadvantage because he or she can no longer send large files. This could get the Exchange administrator a lot of phone calls from irate users. However, if you properly communicate the policy, users will understand your reasoning for limiting their mail message size. To persuade users to your way of thinking, you can explain to them that the limit means:
  • Reduced legal liability because of less inappropriate material being sent into and out of the organization.
  • Reduced possibility of e-mail storms by malicious Internet users.
  • Reduced possibility of virus infection by Trojan horses.
  • Less network traffic.
  • Less disk space utilization. This is especially true for the users that copy every message that they receive.

You might also point out that the recipient’s mail server may already have a limitation on it, so the message would bounce regardless (for example, Hotmail.com has a limit of one megabyte).

The result of this limit? You have fewer outages and a faster network—hardly a disadvantage, in my opinion.

Alternatives
If a user insists that an oversized message must be sent, you can relieve the restriction for a specified period of time. Otherwise, here are several alternatives:
  • Set up an FTP server for large files or have the user FTP to the recipient’s FTP server.
  • Burn the data to a CD-R and courier it.
  • Compress the file with WinZip. In the case of text files, compression can reduce the file by half.

Limiting mail size
To specify a limit on the Internet Mail Connector, just follow these steps:
  • Open Microsoft Exchange Administrator.
  • Select Configuration | Connections | Internet Mail Service.
  • In the General tab, select Maximum and enter the limit in kilobytes.
  • Click OK to save the changes.
  • Stop and restart the Microsoft Exchange Internet Mail Service on the server.

Part of administration is avoiding possible problems, and I feel that this is a step in the right direction. Occasionally, I receive a call from a user asking why they received a Non-Delivery Report. After I explain the reasons for the limitation, users appreciate that their Information Systems department is looking out for them, as opposed to looking over them.
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