Requested feature overview description.
Anyone who uploads a post with a conditional_dnp/avoid_posting tag automatically receives a generated Dmail with the following information:

• Informs them which upload is potentially DNP.
• example: "A post you have recently uploaded (post #146523) might be DNP."
• A bolded disclaimer stating that if the uploader has permission to post, they need not worry.
• quote avoid_posting#permissions
• A reminder: "If you find you have posted DNP, flag it as soon as possible; you will not receive a record if you flag your own DNP post."
• Ask them to check the Avoid_Posting list.

Order of importance open to discussion.

Because of the potential for abuse, this message will NOT be sent if the DNP tag is added after the initial upload.

Why would it be useful?

Pros

• Increased awareness of our leniency given to users who flag their own uploads. Greater potential for compliance.
• Potentially fewer instances of users attempting to cover their tracks.
• Fewer records! Maybe.
• May improve quality of sourcing. (commissioners/uploaders might be more inclined to include their permissions)

Cons

• Might annoy commissioners and artists with exclusive permission to post.
• If they are aware of the new automated messages and are absolutely sure they have permission, they could just dismiss the "You have mail" pop-up.

What part(s) of the site page(s) are affected?
Dmail Inbox

It can never really be a bad thing to have a warning/heads up system. +1

I think it would be a better idea to have a error notification than a dmail when they submit the post.

Like "Error: Post contains artist tag that is currently on the DNP list."

dmail seems a bit too much. imo some sort of notification on top of page would be better

I chose Dmails because I figured it might be easier to implement(*). Simple doesn't always equal effective, though.

As long as it's some sort of notification that doesn't go away until it is acknowledged, it's fine by me.

(*) disclaimer: I am not a coder. I am a bird

I'd support the error notification more than the Dmail, though if one option is much simpler to implement than the other one, pick that one.

Red status bar at the top of the page above or below "Post Uploaded" should be entirely possible.

Otherwise I would say do not send the Dmail for mere conditional_dnp.