Recoll has no direct support for indexing Microsoft Outlook data, because, if you are a Windows user, you probably are not a good customer for Linux desktop indexing…​

However, if you have a need to index Outlook data at some point, I can recommend the excellent libpst library and its readpst utility. Using this you can very easily convert the Outlook data into MH or mbox format, and then index the result with Recoll.