Should I answer a question if the information I am about to publish can be useful for others but also can and is very likely to be used for some dark business?
For instance - I was going to make a self-answered question on SO about how to automatically check if a email address exists on Gmail. This information could be useful for the community (I think) but it obviously can be used by spammers to make databases of existing emails.
So I am not sure if I should post it.
Except rare cases, we don't have access to such secrets which could be dangerous in the short, concantrated format what the SE Q&A format requires.
In your example, if my boss would ask, how long would it be for me it implement a tool to check the existence of a mail address on google, I would say, 1 hour.
This question happens quite often on different SE sites (example). The answer is mostly the same: the real dangers are too little.
There are some exceptions, for example, on the security SE, questions about the offensive side of the security are offtopic.
I think, in the case of such rare exceptions, the site knows already the problem and tunes its policies to close them out as offtopic.
So, I don't think that your content would be really dangerous, but I think it would be surely useful, so you can post it. :-)
