Thanks for the advice @gg30340
Contents of the inbox being deleted without reason and without possiblity of restoring? That sounds like a really serious problem to me, especially for a paid-for premium email service!!
On your advice, I have moved two years worth of emails from my inbox into a subfolder of "My Folders" - over 14,000 messages.
Freeing-up this number of items has not solved the problem. I still get the same time-outs searching my inbox. Considering the search function worked fine on my inbox until fairly recently, I'm surprised that freeing-up 14,000 items was not compensation enough.
I shall continue to move blocks of messages over and out of my inbox, into archives of 5 or 10 years of messages, in the hope that the inbox will reach a size that can be searched again. But it's a very jerky time and very time-consuming process!
I am sure the search timeout must have been reduced on this web application. 11 seconds every time seems like a very specific threshold. Earlier this year, when the search funcion worked fine, yes the search results did take some time to appear (maybe 20-30 seconds, from memory) but they did appear and very rarely timed-out.
