How to compress email attachments using 7-Zip

Don't clog up email inboxes unnecessarily

Ever since the computer age began, boffins have worked to reduce the amount of space required by digital data through compression. Take music, for instance. A typical album in CD format uses about 600MB of storage. Converted to MP3s, however, the files are compressed to just 60MB.

MP3 files, Jpegs and Mpeg2 videos all use 'lossy' compression. This reduces file sizes by stripping out data deemed inessential - frequencies beyond the range of human hearing, for example, and sounds masked by other noise. Data is irretrievably lost but, unless the compression is overly aggressive, an MP3 version of a track should be perceptually near-identical to the original.

For data such as text, however, lossy compression is useless. Can you imagine what would happen if you stripped all the spaces out of a Word document? What's required here is 'lossless' compression.

Lossless compression is what the ubiquitous Zip format is all about. Files are reduced in size, but everything is left intact. To decompress a batch of files, simply extract it.

Zip files (also known as archives) have numerous uses, but are perfect for emailing documents and images. Uploading and downloading email attachments can take an age, but compression lessens the burden. Indeed, without compression, some attachments might be too big to email at all. We'll be focusing on compressing files for use as email attachments over the following pages.

Windows comes with built-in Zip support, but this is limited to basic creation and extraction. To unleash the format's full power and flexibility you'll need to use a third-party utility.

The big hitters here are WinZip and WinRAR but, while both are great, neither is free. Once the trials expire, you're expected to dig into your pocket.

Throughout this workshop, we'll be using 7-Zip. This has all the features of its rivals and costs a grand total of zip.

1. Grab the version of 7-Zip most suitable for your operating system. Installation is straightforward - a simple matter of accepting the defaults although, depending on your PC's setup, you might be prompted to reboot.


Step 1

2. Right-click the file you want to compress and select 7-Zip. To compress the file immediately and save the archive to a current folder, simply click 'Add to ""' (where xxx is the file name). To tap into 7-Zip's full range of features and settings, select 'Add to archive'.


Step 2

Page Break

3. 7-Zip includes a wealth of settings but, for the time being, familiarise yourself only with the options under Archive format. The default is 7z, which produces smaller archives than Zip. However, to extract such archives, the recipient will need 7-Zip. In general, you should stick to the regular Zip format.


Step 3

4. Also familiarise yourself with the options under Compression level. The default is Normal, but you can significantly reduce archive sizes by choosing Maximum or Ultra. Resulting compression will take longer - sometimes much longer - so this option is best used by those with particularly speedy PCs.


Step 4

5. If you want to email several files, individually attaching or detaching each one would take you and the email's recipients a lifetime. Instead, 'stuff' the lot into a single, manageable archive. Hold down Ctrl and select all the files you want, then right-click any one of them and use 7-Zip as normal (see step 2).


Step 5

6. Adding a new file to an existing archive is easy - you don't need to build the archive all over again. Right-click the file to be added, select Copy, right-click the archive, then click Paste. The new file will be automatically incorporated. If archive and file reside in the same folder, you can use simple drag-and-drop.


Step 6

Page Break

7. Use the same method to add updated versions of files. When prompted, click Yes to confirm you want to overwrite. Note that when you add files to an archive, 7-Zip compresses them using the Fastest level, regardless of the level originally used for the archive.


Step 7

8. Many email providers enforce attachment size limits. When sending lots of files - or one enormous file - you could come unstuck. 7-Zip lets you split archives into multiple parts. Under Split to volumes, simply enter the maximum size, appending K for kilobytes or M for megabytes.


Step 8

9. When you split an archive, 7-Zip will append each part with .00x (where x is the version number). The recipient needs to extract only the first version of an archive. The remaining parts will be automatically stitched together. The recipient will, however, need 7-Zip installed on their system to extract the archive.


Step 9

10. Archives can be encrypted. This is useful when emailing sensitive data to someone who uses a shared PC, for example. To encrypt an archive, simply enter and confirm a password. For the encryption method, we recommend 256bit AES. It's an established standard and virtually uncrackable.


Step 10

Page Break

11. You can also encrypt file names - an option that WinZip lacks. For extra security from prying eyes, select Encrypt file names. This option is available only when using the 7z format, however.


Step 11

12. Why not make your archive self-extractable? This will turn it into a file ending in .exe, and all the recipient has to do to extract the contents is double-click it. No experience with compressed files is needed - neither, indeed, is any zip utility. Set the format to 7z, then select Create SFX archive.


Step 12

13. 7-Zip's right-click menu is used to add files from a single folder. To create an archive with files from multiple folders, use the File Manager (Start, Program files, 7-Zip). File Manager has a similar interface to Windows Explorer - to get the best from it, click View then 2 Panels.


Step 13

14. Also in the File Manager, click Tools, Options. Under the System tab, click Select all, ok. This will ensure all files ending in .zip, .7z, and numerous other extensions are directly associated with 7-Zip. Double-clicking a Zip archive will now launch the File Manager, rather than Windows' built-in extraction tool.


Step 14