Trouble with "Outlook"

In the category of "complaints about software" I can add a post about Microsoft Outlook. In principle it is quite a reliable system; many companies and institutions use it for their email system, together with the MS Exchange server. I also have this service linked to my Windows Mobile phone, so I get always push-email, and since several years I have my complete contacts address book (with more than 2000 entries) on there, with sync between mobile and server. Works quite well, and since ActiveSync 4.5 I also seem not to get any duplicate entries anymore.

But recently there have been some issues, and I am wondering what the reason for those problems is and how they can be solved:
- on my Windows mobile the mail arrives now only once per day, although I have set it to deliver as it arrives on the server. Either the server admins have changed the behavior, or I am doing something wrong.
- the Outlook calendar sometimes just pops up pointless meeting reminders: out of nowhere there suddenly comes an alert that I need to attend a meeting - which took place 4 weeks ago! Somehow this alerter seems to go through my appointments, and once in a while finds one for which I have not acknowledged the reminder. This appears to be completely random. I get reminders of events that took place yesterday, last week, a few weeks ago. No idea why this happens, and how to fix it...