Auto Zip Attachments does exactly what the name applies. It adds an AutoZip button to Thunderbird which adds all attachments to an compressed archive, removes the files from the list of attachments and adds the compressed file instead to it. The AutoZip icon will be visible in every compose mail window in Thunderbird. You may override the default behavior of the extension and customize it to suit your needs.

Instead of compressing all attachments into one file you may choose to compress them in separate files or group files of the same type in the same zipped files. It is possible to activate the option to zip files automatically when sending and to prevent that certain file types get zipped at all.