Postbox does not support portable operation.
However, several customers have been able to configure Postbox to run from a portable USB drive, so we're providing information here.
The key is to launch Postbox using the -profile "path" command line argument, where "path" is the location of the profile you want to use. The path should be in quote marks if it includes any spaces. For example, on Windows if the Postbox program is installed on drive F in a folder called "Postbox" and your profile is located in a folder called "My PB profile", you would use this syntax:
"F:\Postbox\postbox.exe" -profile "F:\My PB profile"
The key difference between setting up and running Postbox in this way and doing so in the "normal" way is that Postbox's Profile Manager normally keeps track of your profile(s) using a profiles.ini file stored on the computer's boot drive. For Postbox to be used effectively on a USB stick, in a completely portable mode, it obviously cannot rely upon a file stored on one computer's boot drive in this way. The -profile "path" syntax thus provides Postbox with a way to find your profile without relying on information normally stored on the boot drive.
Note that you can also use the same syntax, even without a USB drive, to run a profile on your computer that the Profile Manager doesn't know about. This can be useful, for instance, if your profiles.ini file happens to get corrupted or accidentally deleted but the profile itself is intact. It would also be useful for roaming users whose profile was on a file share.
If you set up Postbox to store messages on a USB stick, make sure to compact folders periodically. Otherwise, you may find that your mail files on the USB stick are filling up with deleted messages that have not actually been erased from the mail files. Compacting folders will keep the size of your mail files to a minimum.