Using a Gmail account causes a host of issues for your business.

Gmail spam, first off you are missing out on a Branding Opportunity. Your email should use your domain URL such as sales @ yourbusiness.com as the Domain name will be viewed by all recipients.

Customers are 9 times more likely to use a business with a domain-based email.

The Most important reason is Gmail views 67% of email sent to it as spam! Yes, SPAM!
If you send more than a few emails per hour or have multiple emails from the same IP Address, Gmail will more than likely identify your legitimate email as spam and either send to spam box or worse, bounce it back to the sender.
You are at risk of losing clients and never having your important message received.

Read more about Gmail spam and the nightmare it is to fix it.