Let's answer another question from you.
Q: Are you planning Thunderbird integration with Telegram? For in-app chat, or for using as attachment storage?
A: Not right now, because Telegram is closed source on the server side. We want to focus on decentralized, open standard solutions.
To use it as attachment storage, anyone could write a cloud file extension: https://webextension-api.thunderbird.net/en/latest/cloudFile.html
Here are some existing solutions using services like Dropbox and Nextcloud: https://addons.thunderbird.net/search/?q=filelink
@thunderbird
For voice/video chat integration, you COULD add webrtc plugins for things like Webcall servers or Jitsi Meet servers. Here's an example which someone built for Outlook: https://community.jitsi.org/t/plug-ins-for-adding-jitsi-meet-links-to-appointment-requests-emails/21564
