IIRC, new users in Discourse forums are given a message overlay to read prior to creating a new topic.
Many users will want to use an anonymized domain within their topics, which is understandable. However, when they use domains that actually exist (e.g., mydomain.com), it can sometimes be confusing, provide free advertising, or even inadvertently link to malicious sites.
If there is room in the current message, please consider adding something along the lines of the following statement, if one is not already present:
When anonymizing your domain, please use example.com, example.net, example.org, etc. (See Example.com for more information.)
When anonymizing your domain, please use `example.com`, `example.net`, `example.org`, etc. (See <a href="https://en.wikipedia.org/wiki/Example.com">Example.com</a> for more information.)