I've recently begun working as IT/network administrator for a small business who's using Zimbra CS for their e-mail needs.

Now one of the users, the one who's using the mail most I would say, has been complaining for some days that the search doesn't work properly in Outlook. He's using mostly Outlook with the ZCO but occasionally uses the web interface if he has problems with Outlook or works outside the company.

So the problem is whenever he makes a search (Find/Search button) in Outlook, the results come up and some of them (seemingly random) get selected (marked with blue background).
And as he has quite a lot of mail (well kind of, like 2gb) and all of it in his inbox folder and some searches get so many results that the messages list will begin blinking with messages being selected and the search will slow down a lot.

Well I have been doing some tests and have seen the same behavior (messages getting selected without reason) on another computer with another account (also above 2gb) with the same setup (ZCS 5.08, ZCO 5.08/5.11, Win XP, Outlook 2003 SP3 although the rest of the programs are not the same) and could only fix it by upgrading Outlook to the 2007 version.

So I thought I would ask here, see if anybody had the same problem or could figure out what happens since I couldn't find anything anywhere else on the internet. Is that a bug of Outlook 2003 or could it be a problem with the ZCO?
And also: is Outlook search so bad (2003 or 2007) that if you search for several short words it will get any message that has any of those letters combinations in it?

Should I consider maybe changing to Thunderbird with Zindus? Is Thunderbird search better? Will I get all the contacts, calendars, etc synched just like with the ZCO? Has anybody experience changing their users from one to the other maybe?

Well those are a lot of questions, I hope you guys can give me some advice.
Thank you very much for any help.