Transferring Captivate file to another Captivate user?

Yes, just transfer the file which is indeed a zipped folder. That could cause issues because when sending this by a transfer service the cptx extension is sometimes changed automatically in a zip extension, and/or the receiver sees a warning to extract which should never be done. If the extension is changed, it has to be reset to cptx.

If you customized a theme, I recommend to send the theme (cptm file) along. For Preferences this is mostly not necessary. Although Help tells that Mac and PC versions are totally compatible, I had sometimes issues when exchanging cptx files with a Mac collaborator (I am on PC) but not sure that it is always the case.

The Captivate file IS a zip file with a custom extension, so zipping only the Cp file is not value-added. If you need to include other files, like a storyboard, slides, audio files, graphic, etc; it is acceptable to zip them into an archive and email.

If you are talking about files being produced for organizations with security and privacy concerns, you should talk to an account manager or IT representative to get their input prior to choosing a method or service.

Dropbox and cloud file sharing services are worth considering, in areas where fast internet speeds are common. (There are higher risks one you share to the cloud.)

Within a networked environment, sharing the files on a networked drive has benefits. BUT the recipient should be warned that the Cptx file MUST be copied to a local drive before opening within Captivate.

(Sneakernet with a thumb drive is a last option.)

Is it needless to say that backups and version control should be on your mind as you discuss and plan?