I used Yahoo mail's POP server feature (what a mistake) and downloaded all my emails to Thunderbird, only to discover that they had all been deleted from my Yahoo inbox online. Some Mozilla techies helped me to restore my emails from Thunderbird back on to Yahoo Mail using a utility called MailRedirect (mozdev.org - mailredirect: index).
The emails have been restored to the Yahoo inbox, but now when I look at those emails in Zimbra, they all have the same date (the date they were redirected back to Yahoo Mail from Thunderbird, rather than the date they were originally sent). Zimbra shows the correct dates for Sent items etc (i.e. for non-redirected emails).
From what I understand of the MailRedirect utility, it adds another line to the message header called "resent" and maybe "rereceived", so is Zimbra reading the wrong part of the message header? I guess this is an obscure problem, but I'm still in a state of dumbfounded shock that Thunderbird's default mode is the "please delete all my emails" mode....
Any help appreciated.