Contact Form: delete form submissions that contain words from WordPress blocklist

[stephdau]

Is your feature request related to a problem? Please describe.

Currently, the way the Contact Form module apparently handles feedbacks that matches something in the WP Blocklist (Discussion Settings) is:

• Stops the Contact Form notification email from being sent to the administrators.
• Marks the Contact Form submission as spam and would be found under Feedback -> Spam tab

This ends up being very confusing/frustrating to Jp users, because the WP Blocklist is often used to block "toxic users", not just spammers. Putting the message in the spam folder also leads to Jp users reaching out to the Akismet team to enquire about some of what's there, but there is no traces on the Akismet API end of any of the messages that have been processed that way, leading to even more frustrating support experiences.

Describe the solution you'd like

The proposed solution (discussed with @jeherve) is simply for the Contact Form module to respect the standard WP behavior for comments that would trigger the same blocklist rules, put the messages in the Trash folder, and not involve anything Akismet/Spam related.

Leaving the message in the Trash still gives a chance to the site admins to review what is there.

Just as a reference: #430