The end to end principle is a lie. It suggests that instance A either can or cannot reach instance B (unidirectionally).

This does not follow my observations – there is at least one instance that I appear to send my posts to¹ (push from me), it managed to get my updated bio (pull from me), meaning that bidirectional communication should likely be possible. But I don't get its posts (push from it)…

It could also be exponential backoff again, maybe. While the other instance is Mastodon, I already know that my Pleroma creates federation jobs per post, not per remote instance, so those timers are independent here. And I have no idea what Mastodon does w.r.t. broken-and-restored federation…

¹The post has just been sent to the public and to my knowledge, hasn't been interacted with. However, Fedi being Fedi, it technically might be also caused by my server not knowing…