Emails bouncing: why it happens and how to fix it

What is the difference between a hard and a soft bounce?

Every bounce message, also called a non-delivery report or delivery status notification, carries an enhanced status code defined in RFC 3463. The first digit tells you the class: 5 is a permanent failure and 4 is a temporary one.

Not every 5.x.x is about the address. A permanent rejection for policy or authentication reasons, such as 5.7.1 or 5.7.26, means the receiving server refused your message or your domain. Deleting the contact will not fix that; fixing your setup will.

What do common bounce codes mean?

The text after the code matters too. Gmail lists its exact messages in its SMTP error reference, and the wording often names the precise reason, such as an unauthenticated sender or a rate limit.

Why are my emails bouncing?

• Old or guessed addresses. People change jobs, and addresses built from a name pattern often do not exist. This is the most common cause of hard bounces in cold email.
• Typos in the domain. gmial.com, outlok.com or a misspelt company domain.
• Missing authentication. Gmail and Yahoo require SPF or DKIM from every sender, and SPF, DKIM and DMARC from bulk senders. Unauthenticated mail is increasingly rejected outright. Google's sender guidelines list the current rules.
• Sending too fast. A new inbox that suddenly sends hundreds of messages triggers temporary deferrals and, eventually, blocks.
• Reputation or content. A domain on a blocklist, or links to a domain with a poor reputation, can produce 5.7.x policy rejections.
• Full or disabled mailboxes. Usually soft at first, then permanent if the account is abandoned.

How do you stop emails bouncing?

1. Read the bounce message. Find the status code and diagnostic text before changing anything.
2. Separate list problems from setup problems. 5.1.x codes point at the addresses; 5.7.x codes point at your domain, content or reputation.
3. Suppress every hard bounce. Never send to that address again, in any campaign.
4. Verify the rest of the list. Check syntax, domain mail servers, typos and disposable domains before the next send. See what email verification can and cannot check.
5. Fix authentication. Publish SPF, DKIM and DMARC for the sending domain and test with a message to your own Gmail address.
6. Lower the daily volume. Spread sends across inboxes and keep each one within sensible daily limits.
7. Pause if the rate climbs. Find the cause before sending more, rather than pushing through with the same list.

How does Followkite handle bounces?

Followkite reads bounce reports from the inbox that sent the email when it syncs replies. It parses the machine-readable delivery status (RFC 3464) where one is present, and only acts on reports about addresses that inbox actually emailed, so a forged report cannot suppress unrelated contacts.

• Hard bounces (5.1.1, 5.1.2, 5.1.3 and 5.1.10) add the address to the workspace do-not-contact list permanently, with the code and diagnostic, so no campaign can email it again.
• Other permanent failures stop that contact's sequence without suppressing the address.
• Temporary 4.x.x deferrals are left to the mail server to retry.
• Automatic pausing. By default, a campaign or inbox is paused when its bounce rate reaches 5% over at least 20 emails in the last seven days, and the whole workspace is paused at a higher sample size. You can change the threshold or turn this off.

Bounced contacts are marked Bounced in the campaign, and each bounce report appears in the unified inbox with its status code, so you can trace a spike back to a single list import. Followkite does not use SMTP mailbox probing to predict bounces, because catch-all servers and greylisting make it unreliable and it can harm the sender's reputation.