Problem with SEARCH function for Mails

The unified search function across folders and accounts was one of the reasons i chose EM
now it seems to simply not find anything anymore - its a little bit better if i use the advanced search bit still only 20% chance it finds what i am looking for.
Is ther ea size limit for how many mails can be in the Index?
Can i somehow reset / recreate the Index?
Anything else i can do?
Thanx fo you tipps

It may be that you have not selected the folders and fields where some of the results may be, so they are excluded. It can also be that your server is providing the results, which is limited to 100 results.

You can click the down arrow in the search box and select the most inclusive options, but untick the server search, then try the search again: