Pack Attachments

If you're a Microsoft Outlook user looking for ways to free up email space, you can try Pack Attachments, a simple-to-use add-in that finds email attachments and compresses them to create ZIP archives. It requires minimum configuration and can be quickly integrated with MS Outlook.
To get started, it's necessary to set up your Outlook account and choose the folders that will be scanned for email attachments. You can pick anything when it comes to the inbox, drafts, sent, trash, archives, deleted messages, and any other locations.

Compress Outlook attachments into ZIP archives to make room for new data

In the following step, you just have to allow the utility time to find and process all attachments, in order to generate ZIP archives. A couple of settings can be changed before doing this, though, namely permitting Pack Attachments to proceed with the execution even after encountering errors and to decrypt secure messages.
Once the task is over, you can take a look at any email with attached messages to see that they are now packed in ZIP files instead. All ZIP archives are named "attachments.zip". Unfortunately, there are no options integrated for controlling the name of the new ZIPs.

More features available in another, advanced edition

Although there are options described by the developer for filtering attachments by mask and for creating separate archives if there are multiple files attached to one email, these features are, in fact, available in another, advanced edition of the tool, called ReliefJet Essentials.
Pack Attachments compressed email attachments swiftly in our tests and worked smoothly with Microsoft Outlook 2016. We haven't experienced any issues. The tool is fast and easy to use by anyone. However, the free edition doesn't offer more configuration settings over the whole compression operation, which is likely to put off users looking for more control.