The SMTP server is the machine that manages the whole email delivery process. If you are high volume email sender or you want to send 1 million emails per day or want to send 20 million emails per day. Then smtp server gmail, SMTP server hotmail, smtp server aol, smtp server yahoo and smtp server free wont work for you.
You need a dedicated smtp server with multiple dedicated ips and make sure your smtp server setup properly as per compliance with inbox landing with your domain name (i.e spf, dkim, dmarc, rDNS) and your IPs are warmed up and not blacklisted in any spam trapper.
To start sending emails you also need an email marketing software which allows you to manage your email lists, campaigns, suppression lists, and give you full tracking features. And to configure your email marketing software you need a SMTP server host address, smtp username, smtp password and a smtp port number to relay your campaigns.