I think it depends on the price point you are comfortable with . There is Zoho at $2/user, Rackspace at $3/user and then GSuite and Office 365 at $5/user per m

I think it depends on the price point you are comfortable with . There is Zoho at $2/user, Rackspace at $3/user and then GSuite and Office 365 at $5/user per month if paid annually. There is also Namecheap business email from $.90 to $1.50 per user price point depending on how many users you are looking for.