How exactly are your trying to search? There are different possible ways to search with Thunderbird.

I only know of one way, in the search block?

That looks like Global Search. See if this article helps. https://support.mozilla.org/en-US/kb/global-search

Alternatively you can try the Quick Filter Toolbar. https://support.mozilla.org/en-US/kb/quick-filter-toolbar

Can still not search - no results for a message I JUST sent. Global search is enabled.

I am on a Mac running Yosemite, with Thunderbird 37.1.0. My Global Search is also enabled, but I still get NO search results. If my whole email database were too large to search, I would have appreciated a message telling me so. Failing that, it's pretty crippling as I cannot locate anything if I don't know exactly where it is already!

Can still not search

Have you tried Quick Filter Toolbar as an alternative?

Wrt Global Search, you can try to rebuild the global database. https://support.mozilla.org/en-US/kb/rebuilding-global-database

YES - I can NOT search............. NOWHERE on Thunderbird

i have had this problem frequently a year ago and again now. It may be related to fragmented folders. The problem had occurred after compaction and/or a disk defrag. It occurred just now after a disk defrag. My symptoms are slightly different, i can search, and find a list of emails, but when i select, there is no body, ie it is blank. Support staff need to try a disk defrag of fragmented folders and/or compaction, then search.. What i would like to know is how to rebuild the index completely because i believe that would fix the problem..

What i would like to know is how to rebuild the index ...

All you'd need to do is to read this thread.

ok, Christ1, thanks, you are right but i knew that (deleting sqlite db), and did it once before. I didn't express what i wanted correctly.... What i wanted was an automatic index rebuild button that automates the process. So, my bad.

From time to time disk files get fragmented, and so disk defragmentation is one way of improving performance. What i was meaning to emphasize is HOW the db gets corrupted, and what i and i think others are wanting is for "Gloda" to not fail in the first place because of a de-fragmentation or compaction.. That may be an sqlite implementation "feature". Having to rebuild the Thunderbird index MANUALLY should not be necessary for the reason of de-fragmentation, or compaction..