Last time I tried delta chat they didn't have chatmail so this is new to me.

Kinda surprised to find this on privacy policy of the default chatmail instance:

> unconditionally removes messages after 20 days

Didn't see any warning about this in the GUI or the chatmail page.

Does this mean after 20 days the messages on my app will disappear? or just they'll only be available on my local app after that point?

In any case, that's a pretty big red flag that it's not clear.

It is deleted from the server only, it stays on your devices, and is also synced to new device when you add one.

Where did you see this? Or just learned from experience?

FAQ: What happens if I turn on “Delete old messages from server”?

https://delta.chat/en/help#what-happens-if-i-turn-on-delete-...

Cannot find it now, but that's how it was discussed at the time when chatmail server became a thing. It is also how it is configured in chatmail:

https://github.com/chatmail/relay/blob/96a1dbac08441034c5990...

https://github.com/chatmail/relay/blob/96a1dbac08441034c5990...

You obviously must trust that the server runs this configuration, but you can always run your own chatmail, or regular postfix. (If you don't need "federation" with other mail servers, you don't even need port 25 open).

However, you can also configure your app to delete messages from the server sooner.

The FAQ reads:

»By default, Delta Chat stores all messages locally on your device. If you e.g. want to save storage space at your mail provider, you can configure Delta Chat to delete old already-received messages on the server automatically. They still remain on your device until you delete them there, too.«

https://delta.chat/en/help#what-happens-if-i-turn-on-delete-...

AFAIK, the downloaded messages are not deleted from your app.

So if you don't use the app for more than 20 days, you'll start to lose your oldest messages (that you haven't downloaded to your device yet).