Can anyone elaborate on what a 'DNS failure' is exactly?
I thought it meant that perhaps the email address no longer existed, but one of the email addresses in the soft bounce list I know is an active address. So my theory must be wrong!
It really depends. A lot of the time a DNS Failure means that the domain itself doesn't exist, it's an invalid address but because the server couldn't bounce back it was considered a soft bounce. Other times it was because the domain was having DNS issues at the time of the mailing and couldn't respond, which caused a bounce but would work in the future once the issues are resolved.