How should I reply to important people for my company if they write their emails unprofessionally?

I have received and email from a potentially important person for my company. I don't mean the daily spam. I mean verified bigger company CEO. And this email is written in a style you would expect from a teenager.

eg:

"would you be interested in selling your app "

No Hi {name}

No introduction

No Thanks|Regards

No capitalization...

My question is, should I reply professionally, or in a similar style to their?

I know it's good to be professional all the time but isn't there an advantage to writing in a similar way to their level, in order to connect with them more and not to sound like I'm trying to show them how should be done and offend them?

You should reply in a professional way. Or at least in your usual way. Keep your company style. If the person is a CEO of an important company, he can probably permit himself to write such a mail. It's maybe his personal style - not sure he would appreciate your answer in the same style. He could take it for imitation or worse, for parody. And I am sure you don't want to give such an image.

BTW: you don't know conditions in which the message was written. Perhaps he wrote it during some reception from his smartphone...

Keep in mind that he is a boss of an important company and not a baby/teenager. So stay professional. It's known that you may adapt your communication style to the audience but this is not a case of some "geeks conference". By making your message less professional, you have more to lose than by keeping your usual style.

Well what you see above is likely to be an ever increasing problem in business. That problem is the "Texting" culture finding itself into business communication. Although, I'm split on opinion on this issue, in most cases in case of first email I believe it's wrong.

That said I would suggest your reply to be very professional. This will show a few things to a perspective partner:

1. You don't allow your emotions to get in the way of business. Why do I say this? Because to most people getting a one liner like this, especially in regards to their "baby" will be insulted. They will think that the writer is A. Not finding them worthy of introduction, or basic communication Techniques or B. feel that they are a part of the pool of perspective partners, the FORM mail issue. A professional response shows you can maintain that professionalism no matter what. People in fact will at times do this purposely to test a response to see if they want to deal with the person/company.

2. Another reason, is it shows you are professional and sets the stage for further dealings. The person on the opposite end will get a sense that in order to deal with you they will need to treat you as a peer not a subordinate, this does happen a lot in Acquisition scenarios, and believe me you want to be in the Peer group.

3. Even if the deal doesn't work out, maintaining a professional stance at all times will embed it in this person's subconscious and set up roots for long term dealings. This I would argue is the most important thing about being professional 100% of the time. Building your reputation is very important especially as a Startup.