By default, IMAP accounts might only download full messages when you click on them. To force a complete download of all folders and their contents:
Downloading all your emails in Thunderbird ensures you have a local, searchable copy of your entire communication history, which is vital for offline access, migration, or creating a permanent backup. While Thunderbird syncs with servers automatically, it often only fetches headers (summaries) rather than full message content and attachments unless configured otherwise. Step 1: Enable Full Offline Synchronization thunderbird download all emails