The primary danger is that a password leaked from one service might work on another (e.g., banking or social media) if the user reuses credentials.
The "300-K" suggests the file contains approximately 300,000 unique records . 300-K HQ-Mail-Access .txt
If you are concerned that your data may be included in such a list: The primary danger is that a password leaked
Files like these are often distributed or sold on dark web forums and Telegram channels. 300-K HQ-Mail-Access .txt
These are standard plain-text files designed to be fed into automated tools for credential stuffing . Security risks and implications