Bot user vs Webhooks and Slash Commands

Hi, I have a separate “bot server” that accepts POSTs as messages from clients like slack or in this case mattermost and it generates POSTs as responses for them. The way I got the communication going was to set up an incoming webhook so my server could send messages to matterhost, and an outgoing webhook and slash command with my server URL to be able to send messages from mattermost to my server. My question is related to bot users … is there a way that I can make a bot user work like an outgoing webhook? So everytime someone write to this bot user from any channel or directly to it, it triggers a POST request to my server? and then hopefully from my server using the API I can use the access token to answer on behalf the bot user?

The closest I get to a user to be able to write to my server from mattermost is using an specific channel with the outgoing webhook and the slash command from any channel, but I want him to be able to talk to the bot user and that this bot user just POST the message to my server without any plugin installation… is this possible?