An admin or the bot's owner can post bot messages to other users regardless of whether they have subscribed to it.
Here are the following cases on how bot messages will be posted to other users.
Case 1 - When the user has already subscribed to the bot
Case 2 - When the user has not subscribed to the bot.
When a message is posted from the bot, users will see a receive a bot message and a notification at the bottom stating, "You have not subscribed to this bot!", along with two options: