can't send out e-mails from Plesk 9.2.2 server

[StefWeidm]

I have a problem on a recently upgraded server that now runs Plesk 9.2.2, all users from all hosted domains can't send mail from their e-mail clients.

I know Plesk used to use qmail, but now errors from postfix appear in the maillog. Did the upgrade of Plesk cause the change from qmail to postfix? I got very used to qmail over the years, now I have no idea what is going on.

Webmail / Horde is also not working, so clients can't send any e-mail out at all.


Error in the /usr/local/psa/var/log/maillog when trying to send from e-mail client:

Sep 10 06:01:07 wmx-us-08 postfix/smtpd[19237]: connect from unknown[61.xx.xx.xx]
Sep 10 11:01:09 wmx-us-08 postfix/smtpd[8509]: connect from unknown[127.0.0.1]
Sep 10 11:01:09 wmx-us-08 postfix/smtpd[19237]: NOQUEUE: client=unknown[61.xx.xx.xx], sasl_method=CRAM-MD5, sasl_username=sendinguser@hosted-domain.com
Sep 10 11:01:09 wmx-us-08 postfix/smtpd[8509]: 536C77600CA: client=unknown[61.xx.xx.xx]
Sep 10 06:01:09 wmx-us-08 before-remote[20891]: check handlers for addr: sendinguser@hosted-domain.com
Sep 10 06:01:09 wmx-us-08 before-remote[20891]: check handlers for addr: receipient@yahoo.co.uk
Sep 10 06:01:09 wmx-us-08 before-queue[20890]: check handlers for addr: sendinguser@hosted-domain.com
Sep 10 06:01:09 wmx-us-08 before-queue[20890]: check handlers for addr: receipient@yahoo.co.uk

The error in horde when sending mail is:

There was an error sending your message: Failed to open sendmail [/usr/sbin/sendmail] for execution.