[imp] Error when sending mail from a Compose window

[Michael Dahlberg]

I'm running
    Horde 3.0.2
    Imp 4.0.1
 
on a Solaris 9 system.

In the Horde setup, I have configured the Mailer to use the sendmail 
binary and the path is correct and it does work.  I have tried sending 
several messages from this system manually and they are sent without errors.

When I try to send a message from the Compose window within Imp, an 
error message is returned:
    "There was an error sending your message: sendmail returned error 
code 255"

However, the message is sent, but a copy is not stored in the sent-mail 
IMAP folder.  I have the logging option set to debugging level and I get 
the following entry listed in the syslog:

[imp] sendmail returned error code 255 [on line 904 of "/usr/local/share/apache/webmail/horde-3.0.2/imp-h3-4.0.1/compose.php"]

I've looked at line 904 of compose.php but it looks to be a little vague 
about the possible error.

The mail log (also set to the debugging level within the syslog daemon) 
shows no errors or problems other than the following line:
       Authentication-Warning: horde.bucknell.edu: www set sender to 
dahlberg at bucknell.edu using -f

Any suggestions would be most apreciated.

Mike Dahlberg