How to convert Thunderbird to Spark Mail on MacOS? Simply download and use the latest Mac Thunderbird Converter tool, it helps you to convert Thunderbird to Spark Mail on MacOS all along with complete Thunderbird details such as; emails, contacts, and calendar items. The software supports converting batch files from Thunderbird to Spark Mail with no data loss at all. Working DEMO is available, download the Mac Thunderbird Converter free tool to test its working efficiency, it supports converting 20+ files at a time.