It seems what you are requesting is somewhat redundant of the very main feature of posting via email, which is the use of “secret email address”, where only emails to this address will get posted. I mean if you guard your secret email address good enough, you should not be needing this feature at all.
With that said, I do however envision some scenarios where such function may be needed, for instance if you plan to give your “secret” email address to someone else and/or for better “guarding” of it.
Here is what may help:
I believe you should be able to accomplish what you need simply by setting filters in some of your “other” email box (which you CAN give to others). Such filters may include email forwarding, which is where your secret email comes in. Gmail filters for instance will allow you to do exactly this. Just input the desired string in such filter and then only the desired emails will be delivered to your secret email for publishing.
I guess you can also play even more with double email forwarding if for instance you want to publish on per-different-author-basis…
