Campaign Monitor built its reputation on beautifully designed emails and an interface that agencies and marketing teams actually enjoy using. Drag-and-drop templates, solid segmentation, and clean reporting make it a favourite for brands that care about how their email looks in the inbox. But none of that design work matters if the email never reaches the inbox in the first place.
Campaign Monitor monitors your bounce rate on every send, and it is not shy about acting on it. A sudden spike triggers automated deliverability warnings, and sustained high bounce rates can get your sending throttled or your account paused while their compliance team reviews your list. The root cause is nearly always the same: contacts that entered your list through signup forms, CSV imports, or integrations without ever being validated at the point of entry.
This guide walks through exactly how to clean your Campaign Monitor list and keep your bounce rate in the safe zone.
Why Bounce Rate Matters So Much in Campaign Monitor
Every hard bounce is a signal to inbox providers like Gmail, Yahoo, and Outlook that your list hygiene is slipping. Accumulate enough of those signals and your domain reputation drops. Once that happens, even your genuinely engaged subscribers stop landing in the primary inbox. They get filtered into promotions, or worse, into spam.
Campaign Monitor sits on top of shared and dedicated sending infrastructure, which means your reputation affects more than just your own account. That is why their compliance thresholds are strict. A bounce rate creeping above 2% is enough to trigger a warning, and 5% or higher can suspend your ability to send while the account is reviewed.
Soft bounces, the temporary failures like a full mailbox or a server that is briefly unavailable, are less dangerous but still worth watching. An address that soft-bounces on several consecutive sends is almost always dead and should be treated the same way you treat a hard bounce.
The Two Types of Problematic Contacts on Your List
Before you clean anything, it helps to know what you are actually removing.
Hard bounces are permanent failures. The mailbox does not exist, the domain has lapsed, or the account has been shut down. These addresses will never deliver and should never be mailed again.
Risky or catch-all addresses are the harder category. These are addresses on a domain whose mail server accepts everything sent to it, whether or not the specific mailbox is real. They might deliver cleanly, or they might bounce silently days later. B2B lists in particular fill up with these, because so many companies run catch-all routing on their business domains.
Standard email verifiers mark catch-all addresses as “unknown” or “accept-all” and hand the decision back to you. For a Campaign Monitor sender with strict thresholds, that ambiguity is a real problem. You need a tool that can actually confirm whether a catch-all address is live rather than guessing.
Step 1: Export Your Campaign Monitor List
Log in to Campaign Monitor and open the client account that holds the list. Go to Lists & subscribers, select the list you want to clean, and use the Export option to download your subscribers as a CSV.
Campaign Monitor lets you export active subscribers, unsubscribed contacts, and bounced contacts separately. For cleaning purposes, focus on your active subscribers, since those are the addresses that will be mailed on your next campaign. The export includes the email address, subscribe date, and any custom fields you have collected.
Step 2: Validate the List with Scrubby
Once you have your CSV, upload it to Scrubby. Scrubby specialises in the exact category standard validators give up on: catch-all and risky addresses. Instead of labelling them “unknown,” Scrubby tests deliverability at the mailbox level and classifies each address as deliverable, undeliverable, or risky with a confidence score.
The result is three clear buckets you can act on immediately:
- Safe to send: confirmed deliverable addresses you can mail with confidence
- Do not send: hard bounces, invalid addresses, and known spam traps
- Risky: catch-all addresses Scrubby could not confirm, which you can suppress or route into a re-engagement sequence
A Campaign Monitor list that has not been validated in a year will typically show 15% to 30% of contacts in the risky or invalid buckets. Removing or suppressing those before your next send can cut your bounce rate sharply in a single campaign.
Step 3: Build a Clean Suppression List
After validation, export the “do not send” addresses from Scrubby as a separate CSV. In Campaign Monitor, you can add these to your suppression list under Settings so they are automatically excluded from every future send across the account.
Suppressing is better than deleting. A suppression list keeps a permanent record so that if the same bad address re-enters through a new signup form or a fresh import, Campaign Monitor blocks it automatically instead of letting it quietly damage your next send.
For the risky bucket, take a different route. Build a segment for those contacts and send a single re-confirmation email before your next main campaign. Anyone who opens or clicks gets promoted back to your active list. Everyone else stays suppressed until they show a sign of life.
Step 4: Add Real-Time Validation to Your Signup Forms
Cleaning an existing list fixes today’s problem. Preventing bad addresses from entering in the first place fixes it permanently.
Campaign Monitor’s subscribe forms and API do not validate deliverability at the moment of signup by default. You can close that gap by connecting Scrubby’s API to your forms so each address is checked the instant a visitor types it. The API returns a verdict in under a second, letting you block invalid addresses and nudge the visitor to fix an obvious typo before they ever hit your list.
If you are capturing leads through cold outreach or booking calls, it is worth validating those addresses too before they ever reach Campaign Monitor. Teams running calendar-based outreach with a tool like Kali get the most value when the email list feeding it has already been scrubbed, since a clean list means fewer wasted invites and a healthier sending domain.
Step 5: Set a Cleaning Cadence
Even a healthy list decays. Industry data consistently shows that 20% to 25% of email addresses go bad within a year as people change jobs, abandon old accounts, or stop using an address entirely.
For most Campaign Monitor senders, a quarterly clean is the right rhythm. Higher-volume senders, or anyone running paid acquisition that pushes large batches of new contacts into their lists every week, should validate monthly.
A reliable trigger for an unscheduled clean: any campaign where your bounce rate crosses 1.5% for the first time. Acting at that point gives you room to fix the list before Campaign Monitor’s automated thresholds flag the account.
Combining Campaign Monitor Segmentation with Validation
One underused tactic is pairing Campaign Monitor’s engagement segments with external validation. Campaign Monitor lets you segment by opens, clicks, and activity date. Filter for subscribers who have not opened anything in 180 days, and you have isolated your highest-risk cohort for stale or dead addresses.
Run just that segment through Scrubby before a major send. You validate the fraction of your list most likely to cause bounces rather than paying to re-check every contact, which keeps your costs down while still protecting your sender reputation where it counts.
What a Clean Campaign Monitor List Looks Like
After a proper clean, you should see:
- Bounce rate below 1% on most campaigns
- Open rates rising, because a smaller, genuinely engaged list lifts the percentage of people who actually open
- Lower spam complaint rates, since fewer uninterested or mistyped contacts are receiving your email
- Steadier inbox placement, as Gmail, Yahoo, and Outlook reward the strong engagement signals a clean list produces
The link between list quality and deliverability is direct. Every invalid address you remove nudges your sender reputation up, and those gains compound over months of consistent sending.
A Note on Risky Emails for Agencies and B2B Senders
Campaign Monitor is popular with agencies managing multiple client lists, and agency lists tend to carry a high share of catch-all B2B addresses. That happens because so many companies run Google Workspace or Microsoft 365 with catch-all routing, so the domain accepts mail at any address.
Standard verifiers flag all of these as unknowns and tell you to skip them. That advice is safe but expensive, because it means excluding a large slice of real, reachable decision-makers from every campaign. Scrubby’s catch-all verification actually probes those addresses to determine which are live, so you can mail the real ones and suppress the rest. For an agency judged on the results it delivers per client, recovering those otherwise-discarded contacts is one of the highest-ROI moves available.
If you manage Campaign Monitor lists and have never validated your catch-all contacts, that is very likely the single most valuable action you can take on your email program this quarter.
Summary
Cleaning your Campaign Monitor list is not complicated, but it does demand the right tool. Standard validators leave money on the table by dismissing catch-all addresses as unknowns. A specialist like Scrubby resolves that ambiguity and hands you a cleaner, more actionable list.
The workflow: export from Campaign Monitor, validate with Scrubby, push the suppressions back, add real-time validation to your forms, and hold a quarterly cleaning cadence. Run consistently, it keeps your bounce rate low, your account clear of compliance flags, and your beautifully designed emails landing exactly where they belong.
Amit S.
Marketing Lead