Would a legitimate journal send unsolicited email to an author offering to feature an article in their own publication, for a fee? I have received an email from a journal in the field of engineering saying that they found an article of mine and want to feature it in their own publications for a fee.  I cannot tell if this is something legit or something they send to everyone they can find.  I have Googled, but there is not much information on them.  How can I tell?
Absolutely not.

While open-source journals can charge authors to help recoup the publishing costs in the absence of paid subscriptions, it is completely dishonest for a journal to "republish" a work that has already appeared in print. It is even more dishonest for them to charge you to do it. At best this is just an advertising service; at worst it's a scam.

I wouldn't even dignify the email with a response. Send that email into your junk folder.