Cannot read .rpmsg attachment

Hello,

I trusted source sent me an email with .rpmsg file which I cannot read. I tried a few online readers but none of them worked. I want to try to install Outlook and read it but the current version on the App Store is not compatible with the OS version I have. I am running OS 11.7.1. Is there an offline Outlook downloader I can use? Or does anyone know an alternative method I can try. Thanks.