I can, and will, get into this on the Chat Subgroup if you open a new topic there and, as part of that, describe what you want to be seeing after you do a search (in general terms).
I suspect that you're wanting a list of messages just like you'd have in your inbox, but limited to those that match the search. In which case, you'd need to activate the Show results as list control on the initial results page. You may also wish to switch the sort by from relevance (default) to date before doing so, if you're interested in date sorted message order.
That's all I'll say here, as none of this is directly related to NVDA but to Thunderbird.
Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042
The depths of denial one can be pushed to by outside forces of disapproval can make you not even recognize yourself to yourself.
~ Brian Vogel