What is single opt-in?

Single opt-in (SOI) is the simpler of the two main subscriber-acquisition patterns. Users submit a signup form and are added to the active list immediately, without any email confirmation step.

Benefits:

• Zero friction. Every completed signup makes it to the list.
• Simpler funnel, better for measurable conversion rates.
• No confirmation-email deliverability risk (no email step to fail).

Risks without other safeguards:

• Admits typos like john@gmial.com.
• Admits disposable email services trivially.
• Admits malicious signups (someone signing up an enemy or competitor to spam them).
• In some EU jurisdictions, does not meet strict GDPR consent standards.

The standard mitigation is real-time verification on the form itself. Wiring our single-verification API into the signup flow blocks bad addresses synchronously at submit time. That gets you much of the benefit of double opt-in without the conversion drop-off. See should I use double or single opt-in.