Campaign Monitor List Import: Verify Subscribers Before You Upload

To import a list into Campaign Monitor cleanly, export what you have, remove unsubscribes, bounces and anyone without permission, verify the remaining addresses, and upload only the valid rows through Add new subscribers, in files of 20MB or less. Campaign Monitor expects bounce rates of 2% or less from a well-kept list, and suspends sending automatically above a 0.5% complaint rate.

Everything below is from Campaign Monitor's help centre, read on 2 November 2026.

Campaign Monitor's rules

Rule	What Campaign Monitor says	Source
Expected bounce rate	"should typically see bounce rates of 2% or less"	High bounce rates
Complaint warning	First warning when one email passes 0.2%	Suspension for complaints
Complaint limit	"Our spam complaint rate limit is 0.5%"; sending suspended automatically	Same page
Upload size	"20 MB per upload"	Import subscribers
Permission	Importing without permission "may result in the immediate termination of your account"	Same page
Third-party lists	"you cannot use any kind of third party list"	What counts as permission
Old customers	Over a year without email "is a no go zone"; 6 to 12 months, send a reminder first	Same page

Bounces and complaints are linked. Lists that bounce a lot tend to be old, and old lists are where people have forgotten you and press "spam". Verifying removes the dead addresses; the permission rules cover the rest.

How Campaign Monitor handles bounces

From the bounced emails report: hard bounces are "automatically removed from your subscriber list" and added to the suppression list. After five soft bounces with no opens or clicks, an address is treated as a hard bounce. Delivery attempts are limited to a 12-hour period.

That keeps a dead address from being mailed twice. It does not stop it bouncing the first time, which is the bounce that counts against an import.

Step 1: Export the list

From export subscribers:

1. Go to Lists & subscribers and open the list.
2. Click the … menu at the top right and choose Export list.
3. Choose the subscriber type: Active Subscribers for a clean-up, or All Subscribers if you want statuses too.
4. Choose CSV, select the fields and click Export subscribers.

Each list exports as a separate file. Segments have their own Export segment button. Before re-importing later, set "Date added" to "Nothing (skip this field)" in the mapping.

Also export the suppression list: Lists & subscribers, then Suppressions, then Export list (suppression list). Its reasons are Unsubscribed, Marked as Spam, Bounced, and Suppressed for ones you added.

Moving from another ESP? Export there instead; see our guides for Mailchimp, Constant Contact and Brevo.

Step 2: Remove people you must not mail

• Suppressed addresses. Campaign Monitor will not import them, but strip them out of your master file with compare email lists so other tools do not get them either.
• Deleted subscribers. Campaign Monitor warns that re-importing a Deleted subscriber sets them back to Active, and suggests exporting "Deleted Subscribers" first to check. Remove them from the import file unless they really re-subscribed.
• Anyone without permission: trade-show badge scans, partner lists, customers you have not emailed in over a year.
• Duplicates, with remove duplicate emails.

Step 3: Verify

Upload the file on the verify page. Each address gets a live mailbox check and your other columns stay in place. A sample can go through the CSV email verifier first.

Result	Import?
Valid	Yes
Catch-all	Yes, with a custom field value so you can segment
Unknown	Hold; re-check in a day or two
Invalid	No; add to Campaign Monitor's suppression list
Disposable	Usually no

Invalid addresses are worth adding to the suppression list rather than just deleting, so a future import from an old file cannot bring them back. Campaign Monitor lets you bulk-add up to 50,000 addresses at a time.

Step 4: Prepare the file

• One email per row with a header row.
• Columns for name and the custom fields you use.
• A column called something like Email check with Valid or Catch-all.
• Excel files: only the first sheet is imported, so use CSV or one sheet.
• Campaign Monitor ignores custom-field columns whose first 1,000 rows are empty. If catch-all rows are rare, put the column's non-empty values near the top or fill every row.
• Split at 20MB with the email list splitter.

Step 5: Import only the good rows

From import subscribers from a file:

1. Go to Lists & subscribers, open the list and click Add new subscribers.
2. Drag in or upload the file.
3. Match columns to fields. Create the Email check custom field here if it does not exist.
4. Click Save and continue.
5. Read the import report: Duplicates, Updated, Unchanged and Suppressed.

Imported subscribers get no confirmation email, so the first campaign is the first thing they see from you. Make it recognisable.

Step 6: Send in stages

1. Build a segment where Email check is Valid and the subscriber was active recently, and send there first.
2. Watch bounces and complaints in the report. Under 2% bounces and well under 0.2% complaints means carry on.
3. Send to the rest of the valid segment, then to catch-all in smaller groups.

For customers you last emailed 6 to 12 months ago, Campaign Monitor's own advice is a reminder email first. The re-engagement campaign guide has a template.

Updating existing subscribers later

Campaign Monitor says you can "bulk-update information for existing subscribers by doing a list import to add or replace details", and empty cells do not overwrite existing values (update subscriber details). So a periodic re-check is simple: export Active subscribers, verify, and import a two-column file of email and Email check. Then move newly invalid addresses to the suppression list.

Checklist

• Suppressions and Deleted subscribers kept out of the import
• Only subscribers with permission, emailed within the last year
• Duplicates removed
• Every address verified; invalid ones added to the suppression list
• Email check custom field mapped; files under 20MB
• First send to the valid, recently active segment

Verify before you upload

Upload your list on the verify page. You get 100 free email checks when you sign in with Google, no card, enough to test a sample before the full import. For bigger lists, monthly plans are on the pricing page.