Port 25 has many restrictions, why not using another for a "Chatmail network"?

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You aren’t alone!

Alternative P2P realtime chat method

try this, I use it, it’s very convenient and it’s very easy to add to delta chat

Deltachat can of course run over a variety of networks:

Why Choose Delta Chat Over XMPP?

One technical advantage of Delta Chat over XMPP is delay tolerance. You can put Delta Chat on top of any store-and-forward network and get all the features: encryption, groups, audio messages, WebXDCs etc. In XMPP to use OMEMO you need a publish-subscribe service and to share files you need HTTP upload server or connection to the same network to transfer a file over Jingle. For example, it works over HF radio by copying emails using UUCP: Hermes // rhizomatica You can run email over landline p…

Some tutorials on how to run Deltachat over alternative networks would be a very welcome adition to the forum.