Mozilla has pushed out an update for Thunderbird 12.0 to address: Issues relating to new mail notifications and filtering on POP3 based accounts Occasional startup crash seen in TB 12.0 Issue with corrupted message bodies when using movemail Existing Thunderbird 12 users should be able to update via Help > About Thunderbird or may manually download and install Thunderbird 12.0.1 from here. A reminder, support for Thunderbird 3.1 has ended.