A sending campaign can stop itself partway through, before you've touched anything. This isn't about who agreed to hear from you, that's decided before a send ever starts. It's a deliverability guard watching the send itself for signs it's about to hurt your sender reputation.
The Two Reasons a Send Stops
The guard checks two things against a running send, and only after enough recipients have been processed for the numbers to mean something.
An unusually high unsubscribe rate is the first: a normal send draws a small trickle of unsubscribes, and a spike well above that suggests the message or the audience is wrong for each other. The second is a high rate of suppressed or bounced addresses in the batch, which almost always means the segment's contact data is stale, old addresses, typos, people who moved on. Sending into a lot of bad addresses is exactly what damages your domain's standing with Gmail and Outlook, whether or not any one recipient minded the message itself.
Neither check fires on a handful of recipients. Both wait for a real sample of the send to have gone out first, so a small campaign or the first few minutes of a large one won't trip either threshold on noise.
What the Banner Tells You
When either threshold is crossed, the campaign moves to paused on its own and its detail page shows a banner naming which of the two happened and the actual rate that triggered it. The message is the same either way: your sender reputation is why it stopped, and it's worth a look at the message or the audience before you send any further.
Resuming Anyway
You can resume a self-paused campaign directly from that banner. Doing so doesn't just pick up where it left off, it also raises the bar for pausing again: the campaign now has to get meaningfully worse than the first trigger before it stops itself a second time. That's deliberate, it gives you room to keep sending after you've judged the first pause a false alarm, without leaving the guard unable to ever step in again on the same send.
Avoiding It Next Time
Most self-paused sends trace back to one of two things. A stale segment drives the suppression trigger, so clean up old or bouncing contacts before you send to a list that hasn't been touched in a while. Content that reads as a bulk blast, too many links, a shortened link, an image-heavy layout, salesy phrasing stacked up, drives recipients to unsubscribe faster, and the composer flags these as you write. Spreading a large send across more days rather than firing it all at once also keeps both rates from spiking early in the run.
What to Do Next
- Read a Campaign's Results to watch these rates as a send goes.
- Set Your Sender Identity so recipients recognize who's writing to them.
- Build a Segment to review and refresh who a campaign sends to.