When you send an e-mail to a recipient, it may happen that it is rejected by the receiving server. In such cases, the email cannot be delivered - it be delivered - it "bounces off". This is indicated as Bounce.
The receiving server informs our system that the delivery was not possible. The causes for a bounce can be manifold - there are no uniform standards, and each server can return individual server can return individual error messages.
→ Note: In general, we recommend the measures in the article Optimizing the deliverability of your CleverReach mailings to optimize the deliverability of your newsletters.
Below you will find an overview of typical bounce feedback that we frequently we often encounter at CleverReach:
Erroneous addressing:
| host is unknown / host not found | The email server could not resolve the recipient's domain - it does not exist or is misspelled |
| invalid address / invalid recipient | The recipient's email address is invalid (e.g. incorrect format or typing error) |
| mailbox not found / mailbox is unavailable | The recipient's inbox does not exist or is currently not available |
| no mailbox here by that time | There is no user with this email address on the target server |
| no such user | The specified recipient does not exist on the mail server |
| recipient e-mail address unknown |
The server does not recognize the specified email address. |
| user unknown / unknown user | The user name is unknown to the server - the address is invalid. |
| said: 550 | Error code 550 indicates a permanent rejection, e.g. because the recipient does not exist or spam is suspected. |
The messages said: 550 and said: 553 are often used by some servers as bounce messages due to a spam classification.
Filtering of receiving server:
| mail was identified as spam | The mail server has identified the incoming email as spam |
| only registered users may use this system | This means that the server will only accept emails from known or authenticated users - mostly relevant for outgoing mail servers |
| recipient address rejected | The recipient address was rejected by the server |
| relay not permitted | The server was used to forward emails, but does not have no permission to do so |
Hardware problems with the receiving server:
| error writing message | The mail server was unable to process the message completely or save the message, usually when buffering or forwarding the mail |
| message could not be stored | The email could not be stored in the mailbox or mail queue |
| relay access denied | The server rejects the forwarding of the email because there is no authorization for this. |
Problems with the mailbox
| mailbox does not exist | The mail server could not find a mailbox with this address |
| mailbox has been deactivated / disabled / discontinued | The mailbox still exists technically, but is not active. |
| mailbox is full | The recipient's mailbox is full - the storage limit has been exceeded. |
| mailbox unavailable |
The mailbox is currently not accessible - a rather common error. |
| user has exhausted allowed storage space | User has exhausted the allocated storage space |
Help & Support
If you have any questions or need help, you can always contact our service team.