Thank you, Patrice!
If the app that you've used to generate this .RAR archive is a genuine WinRar, then it should have an option to create a series of split archive files of arbitrary and equal size. The initial chunk file will have the name Chiron.rar, the next Chiron.001, then Chiron.002, etc.
They can be uploaded as separate attachments and then downloaded side by side in a common folder. Now if you try to decompress the initial file that has the .RAR extension, all the others will also be decompressed automatically and concatenated into a copy of original file or folder that you compressed into such a split archive.
I don't remember the exact procedure or command line switches but I think you can look them up in the WinRar user manual or command line help.