Letro — Copyright & Open Source

Copyright

Letro is published and operated by Letro Tech GmbH,
Chaltenbodenstr. 8, 8834 Schindellegi, Switzerland. The Letro product
family consists of:

the Letro iOS application, distributed via Apple's App Store;
the Letro Android application, distributed via the Google Play
Store; and
the Letro service, the Matrix homeserver and authentication
service operated by Letro for users of the Letro applications.

All three products are derived from open-source software developed
by Element Creations Ltd. and New Vector Ltd. (together "Element")
and the other contributors to the upstream projects, modified by
Letro. Letro's modifications are © 2026 Letro Tech GmbH; the
underlying upstream codebases remain the property of their
respective rights holders, whose copyright lines are preserved
verbatim in each upstream repository's source files and LICENSE.

Open Source

Each Letro product is derived from one or more of the following
upstream open-source projects:

Letro product	Upstream	Licence	Used by Letro
Letro iOS	Element X iOS	AGPLv3 / Element Commercial	modified
Letro Android	Element X Android	AGPLv3 / Element Commercial	modified
Letro service	Matrix Authentication Service (MAS)	AGPLv3 / Element Commercial	modified

Letro's modifications, and the combined works produced by Letro, are
licensed under the GNU Affero General Public License, version 3
(AGPLv3).

Corresponding source — the modified Letro forks

The complete corresponding source for every component Letro modifies
is published at:

https://git.postnumber.com/letro

Product	Source	Licence text
Letro iOS	https://git.postnumber.com/letro/letro-ios	LICENSE · LICENSE-COMMERCIAL
Letro Android	https://git.postnumber.com/letro/letro-android	LICENSE · LICENSE-COMMERCIAL
Letro service — Authentication Service	https://git.postnumber.com/letro/letro-authentication-service	LICENSE · LICENSE-COMMERCIAL

Each Letro fork repository contains, for every released or deployed
version: the upstream baseline pin (UPSTREAM_VERSION), a dated
fork-divergence record (FORK_DIVERGENCE.md) — the AGPLv3 §5(a)
modification notice for the work as a whole — the full AGPLv3 licence
text (LICENSE), and the third-party attributions
(THIRD_PARTY_LICENSES.md).

Corresponding source — components used unmodified

Synapse, Element Call and the ESS Helm chart that orchestrates their
deployment are operated by Letro unmodified. AGPLv3 §13 attaches
only to modifications, so no separate Letro source offer is required
for these components; the upstream repositories
(Synapse,
Element Call,
ESS Helm chart) are the
corresponding source for the versions Letro deploys. The deployed
upstream versions are listed at
https://www.letro.com/copyright/upstream-versions.

Written offer of source on physical medium (AGPLv3 §6(b))

In addition to the URLs above, Letro Tech GmbH offers, valid for a
period of three years from the date each Letro iOS or Letro Android
binary is conveyed, to provide the corresponding source for that
binary to any third party who is unable to access the source URL
above, on a durable physical medium customarily used for software
interchange, for a charge no more than the cost of physically
performing this conveyance, on written request to [email protected].

This written offer covers the iOS and Android binaries Letro
distributes through Apple's App Store and the Google Play Store. The
Letro service (the Matrix homeserver, authentication service and
related components operated by Letro) is reached only over the
network, not by binary distribution; for that service, AGPLv3 §13
applies and the source URLs above are the offer.

Third-party attributions

Per-product attribution lists for all bundled third-party components,
with their respective copyright notices and licence texts, are
published at:

The same lists are reproduced inside the iOS and Android applications
under Settings → About → Acknowledgements.

Trademarks

"Matrix" is a trademark of The Matrix.org Foundation C.I.C.

"Element", "Element X", "Element Server Suite", "ESS", "Synapse",
"Matrix Authentication Service", "MAS" and "Element Call" are
trademarks of Element Creations Ltd. and New Vector Ltd.

"Apple" and "App Store" are trademarks of Apple Inc.

"Google", "Google Play" and "Android" are trademarks of Google LLC.

"Letro" and the Letro logo are trademarks of Letro Tech GmbH.

Letro is not affiliated with, endorsed by, or sponsored by The
Matrix.org Foundation, Element, Apple Inc. or Google LLC. References
to "Matrix", "Element" and the other names above on this website, in
the Letro applications and service, and in the Letro source
repositories are made solely to identify the upstream protocol and
the upstream projects from which the Letro products are derived, as
permitted by nominative fair use, and do not imply any endorsement.

Contact

Open-source / licensing questions: [email protected]
Operating entity / imprint: see imprint