Two questions, but in my opinion, two very different answers.
If you are trying “cold emails” — that is, broadcasting a significant amount of uninvited emails simultaneously or in sequence you, of course, are treading into spam territory. In this context, if you are evil, more may be better . . . at least in the U.S. (In Canada, you would be breaking the Canadian Anti Spam Legislation (CASL) and could experience some really nasty — even multi-million dollar — fines.)
I’m not advocating spamming, of course. and thankfully doubt it is cost-effective for architectural, engineering or construction marketing. I mean, really, are you going to choose your contractor because he spammed you? (And those Chinese product or material distributors who hit me up in the middle of the night will not sell me anything, either.)
Now, if the question is rephrased: “Can a cold email work?” the answer can be definitely “Yes”, providing you provide real value to the reader, spend time and energy crafting it, build on relationships and associations, and consider an effective call-to-action.
An effective cold email can be a better starting point than an intrusive phone call or (worse) drop-in unannounced visit because you at least provide some respect for the readers’ time in responding; and it can be easy to answer with a simple follow-up.
The danger in business development, in my opinion, occurs when the “a” goes out of the picture and you develop a rote model without considering the individuality of the reader and really research and understand the potential client’s needs, desires and circumstances. Just a few steps along the way, and you are back to the first question, and straight into spamland.