If there's a problem with an intended email address, the mailbox provider sends Blackbaud a code combination of numbers and text to indicate a soft or hard failure. We organise these codes into failure reason categories to help you understand and correct the problem.
Soft failure categories — Include failure codes which aren't permanent, such as such as mailbox full, inactive account, or network error
Hard failure categories — Include failure codes which are permanent, such as unknown user, address error, or closed account