I'm all for keeping things IC and having OOC courtesy. That said if any metagaming occurs, be sure to discuss with an admin so it can be handled appropriately. We all make mistakes and love talking about the game through discord and sometimes someone may need a reminder.
The sending system is a significant tool for hero and villain alike. To devise plans to lure and defeat your enemies! Not to mention the political benefits of impersonating others pcs or one of my personal favorites, NPCS! Let's work together to keep things in check best we can for the sake of fun. If that requires a specific mention within the rules then I am all for it but I would say it falls under metagaming.