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I found that if users give a bad (non existing domain for example) host name in the email address that sendy doesn't list them as bounce or bad in any way. The bad address stays on this list seemingly being sent mail from the status reports. I can understand that there is no remote server to bounce it, so it isn't a bounce, but is an error. Can sendy mark addresses it finds are bad in some way?
When an email 'bounced', it means that the email address does not exist, it doesn’t matter whether the hostname is bad, it will bounce and will show up as such in your list.