We've had another report on Xbar issue. If you go to File | Options | Advanced within Outlook and set the "Send Mail Immediately" to Off. Outlook will then revert to sending on a scheduled basis or if you push F9.
However, with Xbar installed - this functionality no longer works. If the Send Mail Immediately option is Off - then mail is never sent according to schedule. It will just sit in Outbox (no matter what other settings are set for the schedule). If you push F9 it does force send and does send - it just won't do it on an automatic/scheduled basis.
I'm not sure how useful that feature is - but some people like it obviously ! (had 2 reports so far).