SMTP stands for Simple Mail Transfer Protocol used as a communication protocol for e-mail transmission. Using the procedure called "storage and forwarding ", SMTP moves your email on and across the network. SMTP server allows you to send all sorts of transaction emails, e.g. confirmation email, abandoned cart email, delivery updates, announcements, notifications, etc.
You may be using email for business or personal purposes through the website. You can send bulk emails on messages like marketing, correspondence, invitations, notifications, banners, etc., but your hosting provider has limited outgoing mail or sometimes your messages end up in Junk Mail folder. Sometimes back, I encountered a similar problem with the shared server because the server I was using was blacklisted by the email service provider. So to solve this problem, I searched for a free SMTP server because I am not ready to pay much for the email service because the number of visitors is limited to my site. I've set up a list of free SMTP servers that offer you free services but can be limited to your needs and can be upgraded at your discretion.
Please help me spread this list by sharing it on social media and suggesting me if you can know any other great servers that I missed in this list.