postfix conflicts with opensmtpd

[barracuda156]

Error: Failed to activate opensmtpd: Image error: /opt/local/sbin/sendmail is being used by the active postfix port.  Please deactivate this port first, or use 'port -f activate opensmtpd' to force the activation.
    while executing
"throw registry::image-error $msg"
    ("foreach" body line 49)
    invoked from within
"foreach file $imagefiles {
                incr progress_step
                _progress update $progress_step $progress_total_steps
                se..."
    invoked from within
"registry::write {
            foreach file $imagefiles {
                incr progress_step
                _progress update $progress_step $progress_..."