re: Message search "by sender only" (in addition to "by headers and text" and "by headers only").
Been working with this for about 30 min testing various scenarios. Functionally it works as expected with an unexpected bonus: one can search by name or email. I use several different identities for outbound mail which share the same 'friendly' name. Searching by name yields all my outbound mail while searching by email yields only the items from a specific identity. No doubt the same approach could be used with multiple accounts.
As expected I can also isolate mail from specific senders which is beneficial.
I like the integration of this item with the existing searches; each tap brings an increasing level of refinement. Results can be immediately broadened by swiping (if you have swipe search enabled). Nice.
On a few occasions I was longing for a 'back' control to climb back through the results tree. See what you have created - lol! That's not a shadow request btw - more of a testament to how powerful search has become.
Finally, I used this powerful new search to reapply the hidden gmail 'sent' label to several orphaned messages. Worked like a charm (note: a resync is needed to restore 'moved' items to the 'all mail' folder).