Why?
There is a general opinion that whatever goods and services are provided, they must be paid for by someone.
If you are using Gmail, Yahoo, Hotmail, etc, there will be a cost. It might not be in terms of cash but it could be very expensive – proving the old adage that there is no such thing as a free lunch.
Email is one of the most important communication tools in business and it is important that it reflects the professionalism of what you do.
Your credibility could lie entirely within your email address, because if you have a free account then you might be giving the impression you’re not serious about what you do, or don’t want to stick around too long.
While free addresses can serve a purpose, particularly with private email, anything that takes away your credibility can potentially detract from your reputation.