Should I use my main domain for cold email?

No. Always send cold outreach from secondary domains, never your primary. If a sending domain’s reputation gets damaged by spam complaints or a blacklist, you want to be able to retire it without harming the domain your customers and product email depend on.

Buy lookalike sending domains, authenticate each one, warm them, and treat them as disposable infrastructure. Your primary domain stays clean for transactional and relationship email.