How do ESPs decide to throttle or suspend accounts?

You hit send on a campaign and suddenly your sending rate drops to a crawl. Or worse, you get an email from your ESP saying your account has been suspended pending review. What just happened?

ESPs monitor every account continuously. They're protecting their own infrastructure and the shared IP reputation that every sender on their platform depends on. When your numbers start to look risky, they act fast.

The signals that trigger enforcement

Complaint rates are the fastest trigger. Most ESPs start flagging accounts when complaints hit around 0.1%. At 0.3% and above, automated throttling kicks in at many platforms. Sustained high complaints usually mean suspension. These numbers come directly from ISP feedback loops, so the ESP sees them in near real time.

Bounce rates tell the ESP how clean your list is. A sudden spike in hard bounces (addresses that don't exist) signals that you're sending to an old or purchased list. ESPs typically start restricting sending when hard bounce rates exceed 5%, though some act earlier. They're not just protecting you. They're protecting everyone else sharing that IP pool.

Spam trap hits often trigger the most aggressive response. A spam trap is an address that should never receive legitimate email. If you're hitting traps, it suggests your list hygiene has a serious problem. Some ESPs will suspend the account immediately and require you to explain how those addresses ended up on your list before they'll lift the restriction.

Volume anomalies catch accounts that suddenly jump from sending 500 emails a day to 50,000. Rapid volume spikes are a classic pattern for compromised accounts and spammers warming up on a new platform. Even if you have a legitimate reason, expect a manual review flag.

Direct ISP complaints also feed back to ESPs. When Gmail or Outlook sees patterns they don't like from a specific sender on an ESP's infrastructure, they can communicate that directly. The ESP then has to act or risk their own relationship with those mailbox providers.

How the escalation usually works

Most ESPs follow a staged process rather than jumping straight to suspension. First comes a warning email (sometimes automated, sometimes from a human on their compliance team). Then throttling kicks in, which means your sending rate gets capped. Your emails still go out, just more slowly. If the problem signals don't improve, the account gets suspended and you can't send at all until you respond and resolve the issue.

The jump from warning to immediate suspension usually happens when spam trap hits are involved, when there's evidence of a compromised account sending phishing or malware, or when complaint rates are extremely high in a short window.

What to do if you're throttled or suspended

First, don't just email support asking to be reinstated without doing the work. ESPs have seen that pattern thousands of times. What actually works is showing up with a clear explanation of what went wrong and a concrete plan to fix it.

That means auditing your list for addresses that haven't engaged in the past 6 to 12 months, removing hard bounces immediately, checking how those addresses were collected in the first place, and identifying whether any came from a purchased or rented source. If your internal ESP reputation has taken a hit, the path back is showing the ESP that the underlying problem is solved, not just promising it won't happen again.

If your list is aged or you're not sure what's in it, running a validation pass before appealing is worth doing. It removes the addresses that are causing the most damage and gives you something concrete to show the compliance team. You can run that through RME Clean if you want a clear picture of what to keep and what to suppress.

And if this is happening right now and you're stuck, our SOS hotline is free. No pitch, just help.