Zoho Campaigns enforces specific, hard thresholds on bounce rates, spam complaints, unsubscribes, and spam trap hits. Exceeding these isn't just a warning; Zoho reserves the right to terminate your account without prior notification, so it's worth understanding exactly what each threshold means and how to stay comfortably within them.

The Four Thresholds

Why These Specific Thresholds Exist

Zoho Campaigns runs on shared sending infrastructure across many customers. A single sender with poor list hygiene, high bounce rates, or frequent spam complaints doesn't just damage their own deliverability; it risks the reputation of the wider sending domain and IP ranges other Zoho Campaigns customers rely on too. These thresholds exist to catch a problem early, before it escalates into a deliverability issue affecting everyone on the platform.

What Each Metric Actually Means

Hard bounce rate

A hard bounce means the email address is permanently undeliverable, it doesn't exist, the domain doesn't exist, or the server has permanently blocked you. A high hard bounce rate is a strong signal you're emailing a stale, poorly maintained, or improperly obtained list.

Spam complaint rate

This is the proportion of recipients actively clicking "Report Spam" or equivalent in their email client, rather than simply unsubscribing. A 0.1% threshold is genuinely tight, at scale, even a small number of complaints on a large send can trip it.

Unsubscribe count vs. click rate

If more people are unsubscribing from a campaign than are actually clicking through it, that's read as a sign the content isn't relevant or wanted by your list, regardless of how the contacts were originally obtained.

Spam trap hits and unjustified complaints

A spam trap is an email address that isn't real, planted specifically to catch senders who scrape addresses or use poor list acquisition practices. Even a single hit is treated seriously because it's a strong indicator of how a list was actually built, not just an unlucky one-off.

Keeping Comfortably Within These Limits

• Only email contacts obtained through genuinely consensual means, never purchased, scraped, or long-dormant lists.
• Regularly clean your list of hard-bounced and long-unengaged contacts rather than continuing to send to them.
• Make sure your unsubscribe process is genuinely easy to find and use, a hidden or confusing unsubscribe link pushes frustrated recipients toward hitting Report Spam instead.
• Warm up a new or low-reputation sending domain gradually, rather than sending your full volume immediately.
• Send genuinely relevant, wanted content, since a high unsubscribe rate relative to clicks usually reflects a content or targeting problem rather than a technical one.

What Happens If You Exceed a Threshold

Zoho Campaigns can pause an in-progress campaign automatically if its bounce rate crosses the threshold mid-send. More broadly, and more seriously, exceeding these thresholds gives Zoho contractual grounds to terminate your account entirely, without needing to give prior notice, so this isn't something to treat as a soft guideline.