Where does Hardbounces come from?

Hard bounces are contacts that are disabled by our system to protect the entire shipping process from negative reputation. A hard bounce is deactivated for all address books and can't be written to initially. In order for the recipient to receive a newsletter again, this must be activated by the support.

The formation of a hard bounce is very complex and can only be explained by the technical processes that take place when shipping in several stages:

A newsletter always consists of different elements, like pieces of a puzzle, which together result in a campaign. At first, the technical elements of the mailing are put together and handed over to the shipping server. This shipping server then takes over the dispatch to the receiving server (provider of the email client). If the newsletter was successfully handed over to the shipping server, it will be displayed as "delivered".

After this step, the newsletter is in shipping. It is now waiting for a response from the receiving server. If he accepts the campaign, it remains delivered. If he does not accept the campaign, our system receives an error code.
The error codes vary per email client and therefore can only be roughly classified. Error codes are classified as hard bounces if this is already clear from the feedback or based on past experience. It is an automated process.

Examples of error codes: 

Recipient not found by SMTP address lookup
550 5.1.1 Unknown Recipient
550 #5.1.0 Address rejected.
550 5.2.1 Mailbox is blocked
5.4.7 - Delivery expired (message too old)
25: Connection timed out

After this feedback a renewed attempt to contact the recipient address is pointless. On the other hand some error codes are passed through (soft bounce), only when an error feedback occurs several times for the same address, this address will be deactivated (hard bounce).

Because of this diversity, our system can only respond to the error codes. We can not say why the receiving server returned the corresponding code. Therefore it may happen that some addresses are valid, but for some reason, the server reports the error code and the contact is classified as a hard bounce. In these cases the provider of the email address must be contacted.