Betterbird

Betterbird is a downstream fork of Mozilla Thunderbird. It takes a Thunderbird release, applies a set of patches on top, and ships the result under its own name. The patches are bug fixes and interface changes the project considers worth having and that upstream has not taken, or has not taken yet. It is an independent project and is not affiliated with Mozilla or MZLA.

Because it is Thunderbird underneath, everything structural is the same: the same account types and protocols, the same message store, the same add-on model, the same settings layout. Someone moving over is not learning a new mail client, and the patch set is published in a public repository, so what differs from the corresponding Thunderbird release can be read rather than guessed.

The trade-off is the one common to forks. Betterbird follows Thunderbird's release cadence rather than setting its own, and moving a profile forward to Betterbird and later back to Thunderbird is not a step the project promises will work. Back up a profile before switching.