The "Hire a Freelancer" is not the right section to ask.
Atomic Sender is only good if you already have solid SMTP servers.
There's no best software, it depends on what you want to achieve.
If you have the right skills you can build your own SMTP servers (requires skills, time and some money). if you don't want to mess with SMTP servers use a web automation that allows you to send from Gmail accounts and proxies.
Feel free to send me more details about what you need.