Glossary
Unsubscribe
Also called opt-out.
Last reviewed 18 September 2026
How quickly must an unsubscribe be honoured?
An unsubscribe is a reader withdrawing permission to be mailed, and since February 2024 Google and Yahoo have required one to be honoured within two days, a much shorter clock than the 10 business days the United States CAN-SPAM Act allows.
Two days is the outer limit and there is no reason to use it. An unsubscribe is a single row and the send is asynchronous, so the honest implementation removes the address before it answers the request; the senders who need the two days are the ones running an export to a spreadsheet and an import back, which is also how somebody gets mailed after they left.
Every commercial email carries two exits: the headers, for clients that can operate them, and a visible link in the body for everybody else. The link is not optional, because not every client renders an unsubscribe control, a forwarded message loses it entirely, and CAN-SPAM requires a clear and conspicuous explanation in the message itself.
A message that arrives after somebody asked to leave does not produce a second unsubscribe. It produces a spam button press from a reader who now believes you ignored them, and those are the complaints that move a complaint rate fastest.
See also
- One-click unsubscribe
One-click unsubscribe is a mail client operating the unsubscribe on the reader’s behalf by POSTing to an https URI the sender put in the message headers, with no browser, no confirmation page and no further interaction from the reader, as RFC 8058 defines it.
- List-Unsubscribe
List-Unsubscribe is a message header offering machine-readable ways out of a list, and paired with a List-Unsubscribe-Post header carrying the value List-Unsubscribe=One-Click it is what a mail client uses to unsubscribe a reader without opening a browser.
- Suppression list
A suppression list is the permanent record of addresses that must never be mailed again, holding unsubscribes, complaints and hard bounces, and it is checked before every send rather than after one.
- Spam complaint rate
A spam complaint rate is the count of people who pressed the spam or junk button divided by the mail delivered to that provider over a window it chooses, and Google and Yahoo both name 0.3 per cent as the level to stay under and 0.1 per cent as the level to aim at.
Read next
This term is covered properly in Unsubscribe requirements: one-click, List-Unsubscribe and two days, which is a longer piece on the subject.
Every other term is on the glossary index , the longer writing is in the guides, and what this site itself does is on the home page.
Thinking of writing one of these?
5dayemail hosts a five-to-ten day email course: you write it once, and everyone who joins your list gets one email a day, in order, starting from the day they confirm.
Accounts are opened a few at a time rather than by signing up. Leave your address and you will be written to when the next ones open.
One message, when there is room. No course emails, no newsletter, and the address is not passed on. Ask and it is deleted; what is kept, and for how long, is in the privacy policy.