Clean your Mailchimp audience before import

Why verify before the emails reach Mailchimp

Mailchimp bills by contact and polices deliverability aggressively. When a campaign bounces hard, those addresses are marked cleaned and count against you, and a high bounce rate can get a send paused or an account flagged for review. The addresses most likely to bounce are the ones you never verified: an old export, a list you imported from another tool, a trade-show CSV, or a lead-magnet download full of typos and throwaway inboxes.

The fix is to verify the list before it enters Mailchimp, not after. Every undeliverable address you catch on the way in is a bounce that never happens, a cleaned contact you don't pay for, and a small protection for the sender reputation that decides whether your good subscribers see you in the inbox or the spam folder.

Verifly takes a CSV of addresses, runs a live SMTP mailbox check on each one, and returns a deliverable / undeliverable / risky verdict with disposable, role, and catch-all flags. You keep the deliverable rows, drop the undeliverable ones, and import a clean audience.

Clean a Mailchimp export step by step

1. In Mailchimp, open the audience and use Export Audience (or Export Segment) to download a CSV. Note the Email Address column.
2. Grab a free Verifly key at verifly.email/api/v1/autonomous/register — 100 credits, no card, no captcha.
3. Pull the email column out of the CSV and send it to POST /verify/batch in chunks.
4. Keep rows where result is deliverable. Drop undeliverable. Decide per campaign whether to keep risky / catch-all.
5. Re-import only the clean list into Mailchimp — or archive the undeliverable contacts already in your audience so they stop counting.

import fs from 'node:fs'

// pull the "Email Address" column from your Mailchimp export
const rows = fs.readFileSync('mailchimp_export.csv', 'utf8').trim().split('\n')
const header = rows[0].split(',')
const idx = header.findIndex(h => /email/i.test(h))
const emails = rows.slice(1)
  .map(r => r.split(',')[idx]?.replace(/"/g, '').trim())
  .filter(Boolean)

const res = await fetch('https://verifly.email/api/v1/verify/batch', {
  method: 'POST',
  headers: {
    'Authorization': 'Bearer vf_your_api_key',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({ emails }),
})

const { results } = await res.json()
const clean = results.filter(r => r.result === 'deliverable').map(r => r.email)
fs.writeFileSync('mailchimp_clean.csv', 'Email Address\n' + clean.join('\n'))
console.log(`Importing ${clean.length} of ${results.length} contacts`)