[dev] Custom Message "Message could not be delivered" during recipient failure

[Kambey L. Kisambu]

Hi,I'm using postfix and horde in my mail server setup.On sending
email, the local recipients database  table lookup take place and if
the user is not available, it gives the error notice and unable to
send such email.This is a good idea if the recipient is only one, but
if i have varieties of recipients I'm getting trouble to identify the
unknown user.How can i customize the notification message to popup
with the email address claimed to be unknown?From the Horde logs i can
see the following:-...HORDE: [imp] Message could not be delivered -
the address was not found, is unknown, or is not receiving messages.
<demo at domain.co.tz <demo at demo.co.tz>>: Recipient address rejected:
User unknown in virtual mailbox table [pid 19952 on line 1150 of
"/var/www/htdocs/horde/imp/lib/Compose.php"]But the horde popup
message is only "Message could not be delivered - the address was not
found, is unknown, or is not receiving messages."

Kindly assist on this if anybody has an idea.

Regards,
Kambey