Yesterday I received an email from a customer complaining that a search on a full text indexed mail database does not find attachment names.
I tried this on my mail database on a local replica and also on our server and could see the same result: attachment names are not found.
After opening a case @HCL yesterday, today I received the information, that this regression in well known under the SPR # JCUS975RGX:
SPR # JCUS975RGX => Allow attachments to be found by searching for their file names
This is regression started on V10.0.0 and was working on previous versions.
If you also are facing this problem with Notes/Domino V10.x just open a case and refer to this SPR to increase the weightage for getting a solution.