The Mailchimp system sends only one email campaign at a time to each subscribed contact's address, but a few circumstances may result in multiple deliveries. Multiple deliveries typically affect a small handful of contacts and not the entire audience.
In this article, you'll learn what can cause duplicate messages.
Subscriber Has Multiple Addresses
Sometimes, subscribed contacts sign up for your email marketing more than once, with different email addresses. Contacts with multiple aliases may forward all their mail to a single address to manage their inboxes. If more than one alias is on your Mailchimp audience, the subscriber could receive duplicate messages.
To resolve this issue, search your account for your subscriber's name. If the contact has more than one address in the audience, ask for their preferred email address and archive the extra addresses.
Campaign Was Sent More Than Once
If you send the same campaign to audience A and audience B, a contact who's in both audiences will receive the campaign twice. We recommend managing one audience of contacts to reduce the chances of this happening.
To resolve this issue, you may want to combine your audiences and use segments to target different contacts. A campaign that goes to several segments of an audience is only delivered once.
Listserv Addresses in Your Audience
If a listserv address is in your audience, your contacts who are also on the listserv might get duplicate messages.
To resolve this issue, archive listserv addresses and send to individual recipients only.
Subscriber Server Delivery Issue
If several contacts from the same domain, like Mary@CompanyA.com and Joe@CompanyA.com, receive duplicate campaigns, there could be a delivery issue at their server.
To resolve this issue, ask subscribers to contact their email provider or IT department to troubleshoot.