The simplest way to do this is use a search engine e.g. Google and enter:
(This is also useful for searching GitHub issues, pull requests as a Google search is often more effective than the github.com search functionality.)
Alternatively you can go to https://lists.linuxfoundation.org/pipermail/bitcoin-dev/ and download all the gzip mboxes (the URL scheme is simple, so you write a shell one-liner with curl), ungzip them, cat them together, and then use
mutt -f combined.mbox.
This question was answered by various individuals on IRC.