You may need to repair Thunderbird profile when you start noticing issues like missing emails, folders not displaying correctly, messages not updating, or performance problems such as Thunderbird freezing or crashing. Over time, the profile's index files or mailbox files can become corrupted due to unexpected shutdowns, large mailboxes, or conflicts with add-ons. Repairing the profile — or individual folders — helps Thunderbird rebuild its data indexes and fix minor corruption without deleting your emails. This ensures that your folders display all messages properly, new mail syncs as it should, and the application runs smoothly, helping you avoid bigger problems down the line.