I've not seen this happen yet, but figured I'd draw attention to it just in case, because it can be a little counter intuitive. Apologies if this isn't the right place or this is already in the rules somewhere.

When you post to a community on Yiffit, the post (and any attachements like images) lives on your homeserver, not Yiffit.

If your homeserver allows you to view NSFW but does not allow you to post it, you may be breaking that rule by posting NSFW to a remote instance.

I think (from a quick reading of their rules), pawb.social and lemmy.world allow posting of NSFW, but be careful out there if you're on another instance!