Friendly Correspondence with a Stranger Man

I am an event producer and naturally work with men. Recently, I worked with a Haredi man (getting married in four days) and the interaction was technical. When I met him to transfer payment, he later wrote to me in an email: "I was shocked that you are single, I thought you were at least 30 based on your conduct, etc., it really surprised me, to be honest. Is there no way you are under 25???" My question is whether it is halachically permissible for me to correspond with him in a friendly manner beyond technical matters? Because I am a very emotional person, and it could seemingly develop into other areas... But on the other hand, I am very reserved. And at the same time, I maintain good relations with suppliers because it is very important for my work. Is it permissible to evade in such a manner: :) Experience will answer everything... What does Halacha actually say? Thank you very much!

Hello,
Any connection that is not purely technical is forbidden with any stranger man, no matter how religious he is. Even if it is clear to you that it will not lead to anything forbidden, it is a prohibition in itself.

Moreover, the sages said, "There is no guardian for the prohibitions of intimacy."

This means that if complete distancing is not maintained, we can never say about ourselves or any other person that we will not reach the most serious prohibitions.

Even if it seems to us that it is not possible, and we are God-fearing, it will not help against the trial. The only thing that helps is complete distancing from any personal connection.

Shulchan Aruch, Even HaEzer, Siman 21, סעיף 1
A person must distance himself very much from women. It is forbidden to wink with his hands or feet and to hint with his eyes to one of the forbidden women. It is forbidden to joke with her, to behave lightly, etc.