Adding your Gmail address to ConnectionSphere is a good starting to start playing with cold email campaigns.
Most probably, you don't want to risk your own address, or you want to add more addresses in order to scale the game.
This article is about buying Gmail addresses to providers, so you can accomplish with that.
New (fresh) Gmail accounts may be blocked right quickly if you start sending cold emails from the first day.
The safe procedure is to:
If the Gmail account is fresh (recently created), then connect your Gmail account to a free warmer like Gmass or Instantly, and keep the warming running for 2-3 months.
If the Gmail account is 3 months aged or more, then connect your Gmail account to a free warmer like Gmass or Instantly, and keep it keep the warming running for 2-3 weeks.
You can buy aged Gmail accounts in some good providers like Woorke, so you can save the 3 months of waiting.