Mailchimp Transactional (Mandrill) Bounce Rate, Reputation and Hourly Quota

What Mailchimp's docs say

From Reputation and Rejections in the Mailchimp Transactional developer docs, read 8 November 2026:

• "Your account's reputation can be Poor, Good, or Excellent, and can adjust in either direction based on your sending behavior."
• "Reputation is largely determined by the ratio of failed to successful sends. For example, the more bounces you see relative to your overall sending volume, the lower your reputation will be."
• "If your account reputation is Poor, your hourly quota won't increase as quickly as accounts with a Good or Excellent reputation." Mailchimp "cannot change either of them manually." Demo accounts have a fixed hourly quota of 25 emails.
• "While all bounces can damage your reputation, hard bounces are weighed more heavily than soft bounces." "Industry standards suggest that your overall hard bounce rate should be below 5% of your total email volume." The docs add that this is a rule of thumb and varies by ISP.
• Bounced addresses join the Rejection Denylist. "Hard bounce rejections last longer than soft bounce rejections." After a rejection expires, sending to the address is attempted again. Rejections can't be removed in bulk; removing one costs "a small hit to your account's reputation".
• Raw bounce details are kept for seven days.
• On complaints: industry standards recommend a complaint rate under 0.1%, and a single direct complaint "can be difficult to recover from".

Why transactional senders still get bounce problems

• Unverified signups. Typos and fake addresses go straight into the users table, and every password reset, receipt or digest bounces.
• Old accounts. A new feature emails users who signed up years ago.
• Marketing through the transactional pipe. A newsletter sent through Mandrill to an old list. Mailchimp Transactional is built for one-to-one messages.
• Repeated soft bounces. The docs note that an address with many soft bounces may be unusable even if it never shows as hard.

Step 1: export the bounces

Search the Outbound activity for bounced messages (filter by bounce type), export them, and look for patterns: one domain, one signup source, one feature. The bounce message analyzer groups pasted bounce text by cause, and the repeat soft bounce finder flags addresses that soft-bounce again and again.

Step 2: clean the source table

1. Export the addresses your app emails (users, customers, subscribers).
2. Dedupe with remove duplicate emails and fix obvious typos with the email typo corrector.
3. Upload to the verify page. Mark invalid addresses undeliverable in your database so your app stops sending. Watch risky ones.
4. Leave the Denylist alone unless you know a bounce was temporary: each removal costs reputation.

Step 3: verify at signup

Check addresses when they're entered so bad ones never reach Mandrill: see verify email on signup in Next.js and the real-time email verification API. API calls are counted per plan and aren't part of Unlimited.

What checking costs

• Starter, $9 a month: 2,500 checks.
• Pro, $39 a month: Unlimited email verification.*
• Business, $99 a month: the first 300,000 checks a month at full speed, 5 seats.
• Agency, $249 a month: the first 750,000 checks a month at full speed, 15 seats, client workspaces.

*Pro fair use: the first 100,000 checks a month at full speed, then slower, never cut off. Unlimited covers email verification, not API calls. See pricing. Check your list free: 100 checks with a Google sign-in, no card.

More reading: Mailchimp bounce rate too high, soft bounce handling, Gmail sender rules for transactional email, and the email verification API.