Hard and soft bounces
To keep your subscriber list up to date and to get the best results from your email campaigns, we recommend you clean the bounced emails from your database following each campaign you send. How you will manage these will depend on the type of bounce you have.
There are two categories of email bounces – hard and soft. A hard bounce will indicate a permanent issue with the recipients email address (e.g. the email address doesn’t exist any more). A soft bounce can indicate a temporary or resolvable issue with the email address (e.g. the recipients mailbox is full).
Automated bounce handling
Some email services providers (ESPs), like NewZapp, will automatically handle your bounced emails for you. If you’re a NewZapp customer we will automatically remove hard and soft bounces from your database. Hard bounces will be removed after a single bounce, however soft bounces will be removed after 3 bounces. If you have a NewZapp account you can customise your soft bounce threshold.
If you don’t have automated bounce handling or would like to go through your bounced email addresses manually to update the contact details in your database below is some information to help.
We’ve taken a look at some of the most common bounce messages and what you should do with them:
4.4.1 – host not responding
- category: Soft bounce.
- issue: The recipients email host is not responding. This could be due to a temporary issue with their network.
- action required: We recommend resending the email as it’s possible the issue is transient. If the email continues to bounce back you should then consider contacting the recipient to update their contact information or remove their email address from your database.
5.0.0 – undefined status
- category: Hard and soft bounces
- issue: This type of bounce is generic and can include bad mailbox, inactive mailbox, policy related, routing errors, etc.
- action required: You will need to delve deeper into the bounce message to identify the reason the email bounced. Generally speaking the bounce reason will appear somewhere within the full bounce message, as highlighted in the example below:
“Status: 5.0.0 (undefined status) Remote-MTA: dns;domainname.com (22.214.171.124) Diagnostic-Code: smtp;550 unknown user X-PowerMTA-BounceCategory: bad-mailbox“Once you’ve identified the reason, you should then take action appropriate to that bounce type.
5.1.1 – user unknown
- category: Hard bounce
- issue: This message indicates the email account doesn’t exist at the organisation or domain the message was sent to. For example if an email sent to
came back with a 5.1.1 bounce, it indicates the ‘username’ part of the email address is no longer valid or is incorrect.
If the bounce was sent to a business email address this could be because the recipient has left the company and their email address is no longer in use. If it’s to general email client address, such as a hotmail.com email address, the bounce could indicate that the users account has been deactivated.
Alternatively the email may have bounced as the username is incorrectly formatted. For example, it should be
or it could be due to a typo in the email address.
- action required: As this is a hard bounce you should remove the bounced email address from your database. We would then recommend contacting the recipient or organisation to confirm the correct email address or get up to date contact details.
5.1.2 – no such domain
- category: Hard bounce
- issue: This message indicates the domain the email was sent is incorrect or does not exist. For example if an email sent to
came back with a 5.1.2 bounce, it indicates the ‘domainname.com’ part of the address is not valid. This could be because the organisation is no longer in operation or has changed their domain name or it could be due to a typo.
- action required: As this is a hard bounce you should remove the bounced email address from your database. We would then recommend contacting the recipient to confirm the correct email address so you can update your database.
5.2.2 – mailbox full
- category: Soft bounce
- issue: This bounce message indicates the recipient’s mailbox has reached its storage limit so your email was unable to be delivered. This could simply be because the recipient has been out of the office and has received a lot of emails or could possibly indicate the account is no longer in use but has not been deactivated so emails are not being read and deleted.
- action required: As this is a soft bounce we would recommend trying to send to this email address again. If the email address continuously bounces back you should consider contacting the subscriber to confirm if it’s still the correct address to send to or removing the email address from your database.
5.7.1 – delivery not authorised
- category: Soft bounce
- issue: This bounce message indicates the recipient may have mailbox restrictions which mean the delivery of your email is not permitted. For example their mailbox may be set up so it only accepts emails from senders on a safe senders list.
- action required: As this is a permissions issue we recommend contacting the recipient to request they add you to their accepted senders list. Once you have been added to their permissions list you should be able to successfully deliver emails into their inbox.
For a full list of all the bounce messages and what to do with them visit the Microsoft website.
Keep your data clean for better results…
In order to maintain your data hygiene, it’s important to regularly go through your bounce emails and update or delete any out of date contact information. If you don’t maintain your data you are potentially wasting your time and resources on out of date email addresses or worse losing valuable contacts by not keeping their information updated. By keeping your database up to date and clean from any redundant email addresses you will achieve better open and click-through rates.