Building a list you are allowed to mail

Where your list came from determines almost everything about how it performs. Consent is not only a legal requirement; it is the mechanism that keeps deliverability alive.

Consent as a deliverability mechanism

People who asked for your email open it. People who did not, ignore or report it. Mailbox providers read that behaviour and adjust your reputation accordingly.

So a list acquired without genuine consent damages your ability to reach the people who did consent. That is the practical argument, and it is stronger than the legal one for most senders.

The law, briefly

GDPR and UK GDPR require a lawful basis. For marketing to individuals in the EU and UK that generally means freely given, specific, informed, unambiguous consent — a deliberate action, not a pre-ticked box, and recorded so you can evidence it later.

CAN-SPAM in the US is more permissive: no prior consent required, but you must not use deceptive headers or subject lines, must identify the message as an ad, must include a physical postal address, and must honour opt-outs promptly.

Other jurisdictions differ again, some more strictly. If you send internationally, the strictest applicable rule is the practical standard.

Double opt-in

Sending a confirmation email and requiring a click. Costs you some signups and buys a cleaner list, verified addresses, evidence of consent, and protection from typos and malicious signups.

Worth it in almost every case where deliverability matters.

What poisons a list

• Purchased or rented lists. No consent, high complaints, and they contain spam traps.
• Scraped addresses. Same, plus a legal problem.
• Adding everyone who ever transacted to a marketing newsletter without asking.
• Bundling consent — "by signing up you agree to receive marketing" is not specific consent under GDPR.

Spam traps

Addresses that exist solely to catch senders without permission. Pristine traps were never real and only appear on scraped or purchased lists. Recycled traps were real addresses, abandoned, then reactivated as traps — which is why mailing people who have not opened in two years is genuinely dangerous rather than merely wasteful.

Set expectations at signup

Say what you will send and how often, then do that. Mismatch between promise and reality is the leading cause of complaints, and complaints are the fastest way to lose the inbox.

What trips people up

• Treating consent as paperwork rather than the thing that makes email work.
• Importing an old list into a new ESP and sending immediately.
• One consent for everything — transactional, product, and marketing are different promises.

You have got this when

For any address on your list you could say when and how they consented, and what you told them you would send.