If one email brought in far more unsubscribes than usual, start with that one send, not your whole email strategy. Open its report and answer four questions: who received it, how many emails those people had from you that week, what the email offered, and whether that matches what they signed up for. Those four cover the causes you can actually change.
The tempting reaction is to email less to everyone, or to stop the newsletter for a month. That punishes the people who were happy with it, and it doesn't tell you what went wrong. Work through the send first.
First, check it's really a spike
Unsubscribes come in every time you send, so compare against your own history rather than a number from a blog post.
- Take the unsubscribe count for the problem email and divide it by the number delivered. Say 2,000 delivered and 30 unsubscribes: 1.5%.
- Do the same for your last ten campaigns and note the typical figure. If those ran at 8 to 10 per send on a similar list (around 0.4 to 0.5%), the 1.5% is a real jump.
- Check spam complaints for the same email. Someone who reports you as spam instead of unsubscribing hurts you more; if complaints rose too, read why a newsletter goes to spam after this.
Some platforms act on these numbers. Brevo, for example, says it can suspend campaigns and the account when emails sent in the last 24 hours show an unsubscribe rate above 1%, a hard bounce rate above 2% or a complaint rate above 0.2% (Brevo's suspension rules). If you're close to your platform's limits, the next send matters more than usual.
One odd pattern to rule out: unsubscribes arriving on days you didn't send, or from emails sent weeks earlier. That doesn't look like a reaction to one campaign. Collect a few examples and send them to your platform's support before changing anything.
The four checks
| Check | What to look at | It's probably the cause if… |
|---|---|---|
| Who got it | The segment or list the email went to. Did it include an imported list, old customers, or everyone instead of your usual group? | Unsubscribes are concentrated in the group that doesn't normally get your campaigns |
| How much they'd had | Every email each person received in the 7 days before: campaigns plus automations (welcome series, abandoned cart, post-purchase) | New subscribers left while still inside the welcome series, or one group got three or more emails that week |
| What it offered | Subject line and content against your usual emails: a hard sale to a list that signed up for tips, a different product line, a new sender name or design | The email was unlike the ones that came before it |
| What they signed up for | The wording on your signup form, popup or checkout box, and your welcome email | The form promised one thing ("monthly tips", "10% off") and this email delivered something else |
If your platform can filter a campaign report by list or segment, the first check takes one filter, not a spreadsheet. If your unsubscribe page asks for a reason, read every answer for this send; a handful of "too many emails" replies settles the second check quickly.
The fourth check matters if you grew your list with a discount popup. Some of the people who joined wanted the code, not the emails. After they've used it, the next sale email is their moment to leave. That isn't a disaster, but it means the unsubscribes are coming from the signup offer, not from the campaign.
What to change, by cause
Wrong audience. Go back to sending this kind of email only to the group that asked for it. If an old or imported list was included, don't put it back into regular campaigns; give it a separate "do you still want these?" email first, the way the re-engagement sequence does.
Too many emails at once. Add a simple frequency rule: nobody gets more than two marketing emails in seven days. Some platforms have a built-in frequency cap; if yours doesn't, exclude people who are currently inside your welcome or post-purchase automations from campaigns.
Content didn't match. If you're changing what you send (adding sales to a tips newsletter, launching a new range), say so in the email before the change, and offer a choice where your platform supports it: "all emails", "only new products", "less often". A preference link gives people a step short of leaving.
Expectations at signup. Rewrite the form so it says what people will get and how often. For example:
Get one email a week: new arrivals and one how-to. 10% off your first order. Unsubscribe any time.
Then say the same thing in the first welcome email. If you don't have a welcome series yet, this one is a short starting point.
Don't make leaving harder
When unsubscribes jump, it's tempting to shrink the unsubscribe link or bury it. Don't. Someone who can't find it may use the spam button instead. Gmail's sender guidelines ask senders to make unsubscribing easy, and larger senders must offer one-click unsubscribe. An unsubscribe costs you one reader; a spam complaint can affect where your next campaign lands for everyone.
A ten-minute check after every send
A day after each campaign, write five numbers into a sheet: delivered, unsubscribes, spam complaints, clicks, orders. Next to them, keep the median of your last ten sends. When one number sits well above its usual range, you'll know the same day, and you'll have the history to see whether it's a one-off or a trend.