Single Opt-In
Single opt-in subscribes an address after one request, without an email confirmation step. It does not verify access to the entered address.
Single opt-in subscribes an address after one subscription request, such as submitting a signup form. The person does not have to confirm through a separate email before the subscription begins.
This removes a confirmation step but leaves ownership of the entered address unverified. A typo or a request submitted by someone else can enter the list. Double opt-in adds an email confirmation that helps check access to that address.
Record what the person requested
Make the sender and subscription purpose clear at signup. Keep the wording shown, the source, and the relevant time and subscription choice. Collect only the additional data you need under your privacy policy. A record of form submission is not, by itself, proof that every legal requirement was met.
Requirements depend on jurisdiction and purpose. Compare the US CAN-SPAM guidance with the UK electronic-marketing rules when choosing the signup flow.
Protect the form and the audience
Check for malformed addresses and signup abuse. Honor unsubscribes and handle bounces before subsequent sends. An import or an account signup does not automatically grant permission for unrelated marketing. Keep the original purpose attached to the record.