Valid email addresses can hard bounce for many reasons. Reading bounce headers (SMTP replies) can provide insight on what caused an address to hard bounce and give a strong indication whether a hard bounced email address should be added back to your list. Below, you'll learn common reasons a valid email address could hard bounce and how to add a hard bounced email address back to your active list.

In this article:

Reasons Valid Addresses Bounce

Denied by Firewall or Filter

If your email was blocked, a spam filter may have interpreted the campaign content as spam. Spam filters can be on the recipient's computer, on their company's email firewall, at their ISP/Data center, or all of the above. Common SMTP replies for spam filtered emails include Denied, Unacceptable Content, Blocked, and similar messages.

If the email address is someone you know, use the Send a Test email option in the Campaign Builder to send a quick, plain-text email to a single recipient. If a "Hi, how's it going?" type of personal message gets through, but your normal email campaign doesn't, it's likely an issue with the campaign's content.

Run your email campaign through a spam filter test program like our Inbox Inspector to see if any issues are noted. Also read our guide on how spam filters think to see if anything mentioned there sticks out about your content.

Is MailChimp blocked?

Corporate spam filters and email firewalls can be very strict and treat a large amount of identical incoming emails as spam. If the spam filter or firewall is used to seeing you send one or two personal emails to a client in the company, they may interpret a bulk send made on your behalf as spam.

A block can be temporary if the recipient email server thinks too much email is coming from one server too fast. Other times the block is permanent and the only way to get around that is to ask the IT group in charge to whitelist MailChimp IP addresses.

Is a major ISP blocking your emails?

If a major ISP like Gmail or MSN/Hotmail is blocking your emails, this is typically only temporary. ISPs usually unblock senders within a day or two after spam complaints subside.

MailChimp participates in many feedback loops with major ISPs and we usually already know when an ISP is blocking any of MailChimp's sending servers. We re-route emails to other outgoing email servers until the issue is cleared up. We'll also investigate the user that caused the problem, and may suspend them if we feel they're doing too much harm or violating our Terms of Use.

If you see a major ISP blocking MailChimp in your SMTP replies, it still helps if you contact us immediately so we can work things out with the ISP directly. 

However, if your From: email address is at AOL or Yahoo and you see a high number of bounces, it is likely that the delivery of your campaign was affected by changes in DMARC policies.

Add a Valid Address Back to Your List

If you determine a hard bounced email address is valid and want to add it back to your list, you must first must delete the hard bounced email address. Once deleted you can resubscribe this address. To add a hard bounced email address back to a list follow the steps below.

  1. Navigate to the Lists page.
  2. Click the title of the list you're working with.
  3. Click the Subscribed drop down menu and choose Cleaned.

    Cleaned option

  4. Locate the subscriber you want to add back to your list and click their email address.
  5. Click the Delete button on the subscriber's profile.

    Delete button on subscriber profile

  6. Click the Confirm button on the Are you sure? pop-up modal.
  7. Click the Manage subscribers drop-down menu and choose  Add subscriber.

    Add subscriber option

  8. Fill in the subscriber's information and select the checkbox for This person gave me permission to be added to my list.
  9. Click the Subscribe button.

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