[89297288]

It doesn't sound like SimpleX solves this either [0]:

> There is still a risk that a server maliciously records all queues and messages (even though encrypted) sent via the same transport connection to gain a partial knowledge of the user’s communications graph and other meta-data.

[0]: https://github.com/simplex-chat/simplexmq/blob/master/protoc...

[sandblast]

> SimpleX supports measures (managed transparently to the user at the agent level) to mitigate the trust placed in servers. These include rotating the queues in use between users, noise traffic, supporting overlay networks such as Tor, and isolating traffic to different queues to different transport connections (and Tor circuits, if Tor is used).

Also, most often the two parties use different receiving servers, and this aligns us more with the physicals letters analogy from the submitted article, except that each receiving server is more like a central post warehouse in a big city and not a small district branch.