Understanding Bounce Rate Errors in Your Email Newsletters

Created by Harmeet Singh, Modified on Mon, 4 Aug at 1:01 PM by Harmeet Singh

What is Bounce Rate?

Bounce rate refers to the percentage of emails that could not be delivered to the recipient’s inbox. These emails are "bounced back" by the receiving mail server and are usually caused by invalid or unreachable email addresses.

What’s a Healthy Bounce Rate?

A healthy bounce rate is below 2%. Higher rates can:

Harm your sender reputation
Reduce email deliverability
Get your domain or IP flagged as spam

We recommend regular list cleanup to keep your bounce rate low.

What Do Bounce Errors Mean?

Here are the most common bounce subtypes and diagnostic messages, with plain-language explanations and what you should do.

Bounce Subtype	Diagnostic Code / Message (Example)	What It Means	What You Should Do
OnAccountSuppressionList	`Amazon SES did not send the message to this address because it is on the suppression list...`	This email address previously hard bounced or marked messages as spam. It’s now automatically suppressed by Amazon SES.	Review and remove these addresses from your mailing list. See SES Suppression List Guide if needed.
MailboxNotFound	`smtp; 550-5.1.1 The email account you tried to reach does not exist.`	The email address doesn’t exist — likely due to a typo, fake address, or deleted account.	Remove the address from your list. If input came from a form, enable double opt-in to prevent typos.
MailboxInactive	`smtp; 550-5.2.1 The email account you tried to reach is inactive.`	The email account exists but is temporarily disabled or abandoned.	Wait and retry once if expected to reactivate. Otherwise, remove it.
MailboxUnavailable	`smtp; 550 Requested action not taken: mailbox unavailable`	The mailbox is currently unavailable, possibly due to technical or server issues.	Retry a few times. If it continues to bounce, treat it as a hard bounce and remove.
MailboxFull	`smtp; 552 5.2.2 The email account is over quota.`	The recipient's mailbox is full and can’t accept new messages.	Retry later. If the bounce persists over multiple days, consider removing or flagging.
InvalidRecipient / UserNotFound	`smtp; 550 5.1.1 <email@example.com>: user does not exist`	The domain exists, but the specific user doesn't. This often occurs when employees leave companies.	Remove from list. Optionally flag for manual review if it's a known contact.
Typo / Format Issue	`smtp; ... double-checking the recipient's email address for typos or unnecessary spaces`	The address may be malformed — extra characters, wrong domain, etc.	Check for typos or cleanup issues. Remove if not fixable.
DomainDoesNotExist	`smtp; 552 1 Requested mail action aborted, mailbox not found`	The entire domain (after @) does not exist.	Remove from list immediately. May be a fake or mistyped domain.
Unknown Google User	`smtp; 550-5.1.1 ... <https://support.google.com/mail/?p=NoSuchUser`>	Google is reporting that the user does not exist.	Remove from list. Cross-check if it's a valid user from your records.
Disabled Google User	`smtp; 550-5.2.1 ... <https://support.google.com/mail/?p=DisabledUser`>	The Gmail account is inactive or disabled by the user or Google.	Remove from list unless you expect the user to reactivate their account.

What Should I Do With Bounced Emails?

Here’s how to handle bounced addresses on your end:

Clean Up Your List

❌ Remove any email flagged as "does not exist", "inactive", or "suppressed".
✅ Enable double opt-in so users confirm their email is correct.
Use an email validation tool to pre-check for invalid or inactive domains.

Avoid Risky Practices

Don’t buy email lists.
Don’t send to old/inactive lists without reconfirmation.
Avoid sending repeated emails to previously bounced addresses.

Why This Matters

A high bounce rate can cause:

Poor inbox placement
Delivery throttling or blacklisting
Messages going straight to spam

Keeping your list clean improves engagement and protects your brand reputation.

Need Help?

If you're unsure how to interpret a bounce error, or want help cleaning your list, feel free to contact our support team with:

The full error message
Bounce subtype (if available)
Email address in question