There is always a cost to security. How much you and your recipent ready to pay?
And, what you mean by “secure”? E2EE is basic. How about meta data? Or resilient to DPI? How about correlation attacks? Then the directory server. And the operator of the server. Where they located can be a factor too.
There can be a milion factors that can contribute to security. You can have it all but I don’t know if such thing exist or not. For each factor, you gain some security but loss some in other places. You need to pick and choose what you need.