Simply put, the server can't verify the email sender.Įmail address does not exist: Invalid emails are the most common reason for hard bounces. the email will bounce.ĭMARC (DKIM/SPF) requirements: Your email message might not meet the recipient mail server’s DMARC requirements for email authentication. Make sure your email isn’t overloaded with GIFs and images, or your email might bounce back.Įmail account temporarily suspended: If the subscriber has not signed in for more than 365 days, or if their server has detected suspicious activity, their account could be locked temporarily. Oversized message: This is rare, but some inboxes have sensitive filters that restrict the message size. If this happens, you can try resending your campaign the next day. Server timeout: The subscriber’s email server may be temporarily unavailable, overloaded, or undergoing maintenance, and any incoming messages will bounce.

If this limit is reached, your email campaign will be bounced back to you. Mailbox full: Some of your subscribers’ mailboxes have limitations in terms of capacity. What are those reasons? We’re glad you asked. Your email tool will successfully send out the email, but then the subscriber’s email server rejects it for some reason. When emails bounce back, it usually has nothing to do with your email marketing software.

Email bounce back message example