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Zip and encrypt Microsoft Outlook email attachments

Available for Microsoft Outlook 2000 and higher, WinZip Companion for Outlook is an affordable third-party program that can be used to protect email attachments -- with your choice of .ZIP encryption.

Not long ago, I wrote a tip called "Microsft Outlook email encryption simplified," which was about a third-party...

application that provides a way to encrypt emails using the .ZIP format.

A number of people wrote to me about a competing product from the makers of the WinZip archiving tool called WinZip Companion for Outlook. Available for Microsoft Outlook 2000 and higher, this affordable third-party program can be used to protect email attachments -- with your choice of .ZIP encryption.

When installed, the program lets you select a series of default behaviors for new messages with attachments. You can have attachments zipped automatically, or be prompted to compress attachments.

Files below a certain size threshold, or that match a list of file extensions, can also be excluded from being compressed. In addition, the program can automatically label or document the archive in question

WinZip Companion for Outlook supports three levels of encryption for attachments, which are listed below in increasing order of strength:


  • ZIP 2.0 (broadly compatible with applications that can read .ZIP files)
  • 128-bit AES
  • 256-bit AES

Not every .ZIP program supports 128- and 256-bit AES. So if you plan to use them regularly, make sure other users can extract them. The vendor has published information about the file format WinZip uses to create AES-encrypted .ZIP files. This makes it relatively easy for programmers to make use of them.

(It might even be possible to write an Exchange Server event sink to automatically extract and decode the attachments, and match against a password stored somewhere in Active Directory.)

As with similar products, your recipient will need to already know the password to extract the encrypted files in question. It would be nice to be able to encrypt the messages based on a public/private key-pair, for instance. But I suspect that feature falls outside of the .ZIP encryption standards and would require a whole new approach.

WinZip Companion for Outlook costs $19.95 per single-user license.

About the author: Serdar Yegulalp is editor of Windows Insight, a newsletter devoted to hints, tips, tricks, news and goodies for all flavors of Windows users.

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