Alright, let me break down how I arrived at the response for this particular message. The user provided a message promoting a Telegram channel's grand opening with a link. My task was to process it according to specific guidelines.

First, I looked at the content. It's an invitation to join a channel, which is promotional. The guidelines mention rejecting messages that are commercial propaganda or spam without news content. This message fits that category because it's advertising a service rather than sharing news.

Next, I considered the formatting rules. Even though the message could be formatted, the content itself is what's problematic. Since it's promotional, it doesn't matter how it's presented—it still needs to be rejected.

I also checked for any other red flags, like mentions or external links. The message includes a link, which should be removed, but the main issue is the promotional nature. There's no news source cited, so it doesn't fall under any exception.

Finally, I concluded that the appropriate response is 'MARKETING_MESSAGE' because the content is spam or commercial propaganda without any news value. This aligns with the guidelines provided, ensuring I follow the rules correctly.

MARKETING_MESSAGE