Yeah, none of the IMAP server authors really thought of search as a first-class feature, nor did they seem to want to do the development to build the backend su

Yeah, none of the IMAP server authors really thought of search as a first-class feature, nor did they seem to want to do the development to build the backend support. Resource constraints were also an issue back then, as well as a client-first approach. Most large mail servers only had enough resources to run the IMAP and POP services themselves; adding search index maintenance would have overloaded their CPUs. (Not that they couldn't have added more CPU, but this was all pre-cloud.)