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What goes on a suppression list?
Numbers that replied with an opt-out keyword such as STOP or UNSUBSCRIBE, numbers whose owners withdrew consent through another channel, complaints and numbers the business must not contact for legal reasons. Many senders also suppress numbers that repeatedly fail delivery, which protects their sender reputation and avoids paying for messages that cannot arrive.
How is a suppression list different from a do-not-call register?
A do-not-call or do-not-disturb register is run by a regulator or an operator and applies to every sender in a country. A suppression list is kept by one business for its own audience. Where a national register exists, check both: a number can be clear on the register and still be suppressed because that subscriber opted out of your messages.
How long should opt-outs be kept?
For as long as you might message that number. Deleting an opt-out record is how numbers get contacted again when an old list is re-imported or a customer signs up a second time. Data-protection laws such as the GDPR allow keeping the minimum needed to honour the objection — the number, or a hash of it, with the date and the source of the opt-out.
Does a marketing opt-out stop transactional messages?
Not normally. A marketing opt-out does not usually stop service messages a customer needs — one-time passcodes, payment alerts or delivery updates — but rules differ by country and the customer's request may be broader. Keep marketing and transactional consent as separate flags, and stop all messages where the law or the customer requires it.