In this Greek tutorial by Leonard Muellner (https://www.youtube.com/watch?v=N_kd_IX2Zec&list=PLq5ea-jR9u2puDaLoRL-nBkpwrkURbLjT&index=73) at about 12:30 he anecdotally mentions a story about Spartans sending a herald or some heralds to the Athenians, who drown the sacred messengers and as a result are cursed by their penises falling off. Initially I assumed this was from Thucydides or Herodotus but I actually haven't found any instances of Athenians drowning Spartan messengers and being cursed this way. The only similar curse I can imagine would have to do with the Alcmaeonids but their penises did not fall off as a result.
I was specifically wondering about such a specific curse because of course eunuchs are similar to heralds in that they have sacred liminality etc. and I was interested in following the thread to see where it leads, but sadly the original source of this story is lost to me. Does anyone else have an idea where it could be from?
edit: nothing in this thread either but still very interesting: https://www.reddit.com/r/AskHistorians/comments/ac7j42/exactly_how_common_was_it_to_kill_the_messenger/?utm_source=share&utm_medium=web2x&context=3
To my knowledge, there is no such story. It sounds to me as though Muellner has fused together three different episodes from the sources. Two of these I have mentioned in the post you linked:
When Dareios sent messengers to demand earth and water from the Greek states, according to Herodotos, the Spartans threw them into a well, and the Athenians into a place called the Pit. The Pit was a hole in the ground where the Athenians deposited the bodies of criminals they had executed (or, alternatively, criminals sentenced to death were thrown into the Pit).
During the Peloponnesian War, the Thracian king Sitalkes, who was an ally of Athens, intercepted a Peloponnesian mission on its way to the Persians, and delivered the envoys over to the Athenians. When the prisoners arrived at Athens they were promptly executed, and their bodies thrown into the Pit. This was done to avenge the Athenian merchants that the Spartans had been capturing around the Peloponnese, executing, and throwing into a pit (Thuc. 2.67).
Finally, a third piece of Athenian history seems to have been mixed in, which has nothing to do with harming messengers but everything to do with sacrilege and detached penises. This is the story of the mutilation of the herms in 415 BC, just before the Athenians sailed for Sicily. These statues, usually shaped as a pillar with a head and phallus, which marked boundaries in Athens and warded off evil from public places, were all found one morning with their erect penises cut off. The sacrilege shook the city and led to a string of trials, exiles and executions of prominent suspects.
In none of these stories do the Athenians throw anyone into a well. I'm pretty sure this is a conflation of the first story with the other two. The Spartans kicked the Persian messengers into a well, but at Athens, as was the custom, they would have been thrown into the Pit. The idea that the messengers were actually sent to Athens is a confusion; they were sent to Persia, but intercepted and brought to Athens as prisoners.
In none of these stories do any actual living Athenians lose their genitals, either. As my other answer shows, the curse that was supposed to fall on people who killed messengers was usually pretty vague - so much so that the Greeks themselves struggled to determine which events amounted to the divine retribution that was expected to follow. There is never such a clear consequence as "your dicks will fall off," which is what makes me suspect that this is a conflation with the famous case of the mutilation of statues. Even Herodotos contains no story as fantastical as to include people suddenly suffering the loss of their own penises. If there was ever any such tale, you would have to seek it in myth.