Domain Age
How long a domain has been registered — older domains generally have better email deliverability.
Domain age is a factor in email deliverability because brand-new domains are frequently used for spam. Email providers give more trust to domains that have been registered for months or years.
For cold email, the recommendation is to register your sending domains at least 2-4 weeks before starting warmup, and at least 6-8 weeks before sending campaigns. Some practitioners recommend aging domains for 3+ months.
Buy domains from reputable registrars, set up a basic website, configure all DNS records (SPF, DKIM, DMARC, MX), and start warmup early. Don't buy expired or previously-used domains without checking their reputation first.