Choosing Between Domain Purchase & Email Services for Campaigns

I've got the choice, through my current employer, to go out and purchase 5-10 domains and start warming them up for email campaigns (through Clay's warmer) or looking at a company like Instantly. Has anyone gone through this before and any feedback on what is a better process? To be honest, the subject of warming up emails is new to me. At a maximum, our team might send out 50 emails a day.