Lookalike (cousin) domain spoofing uses a domain visually similar to yours (examp1e.com, example-billing.com) to send mail that passes authentication for the attacker's domain while impersonating your brand.
How many lookalike domains should I register?
The top 10 to 20 variants by likelihood is a reasonable start; monitoring covers the long tail.
Why does lookalike domain spoofing matter for deliverability?
DMARC stops exact-domain spoofing, so attackers moved to lookalikes. It is now the dominant brand-impersonation technique.
What is the first step to get started with lookalike domain spoofing?
Register the most obvious typo and hyphen variants of your domain.
What is the most common lookalike domain spoofing mistake?
Assuming DMARC p=reject protects against lookalikes.