sending mail error

[Sage McGirk]

After typing an email, i hit the send button.  the page reports:
'There was an error sending your message'

/tmp/horde/log

Jan 23 22:03:17 HORDE [error] [imp] unable to set sender to
[myusername@mydomain.net] [on line 787 of
"/usr/local/apache/htdocs/horde/imp/compose.php"]

/var/log/maillog shows that i've logged in and out twice when i log into
imp


Jan 23 23:18:32 mirage imapd-ssl: Connection, ip=[::ffff:123.123.123.123]
Jan 23 23:18:33 mirage imapd-ssl: Opening smtp relay for IP
[::ffff:123.123.123.123]
Jan 23 23:18:33 mirage imapd-ssl: LOGIN, user=user@mydomainc.com,
ip=[::ffff:123.123.123.123]
Jan 23 23:18:33 mirage imapd-ssl: LOGOUT, user=user@mydomain.com,
ip=[::ffff:123.123.123.123], headers=0, body=0
Jan 23 23:18:42 mirage imapd-ssl: Connection, ip=[::ffff:123.123.123.123]
Jan 23 23:18:42 mirage imapd-ssl: Opening smtp relay for IP
[::ffff:123.123.123.123]
Jan 23 23:18:42 mirage imapd-ssl: LOGIN, user=user@mydomain.com,
ip=[::ffff:123.123.123.123]
Jan 23 23:18:42 mirage imapd-ssl: LOGOUT, user=user@mydomain.com,
ip=[::ffff:123.123.123.123], headers=0, body=0 


any ideas?

horde2
imp3
qmail-1.03

thanks in advance

sage