I have the same issue, a user is supporting many of our customers and need a way to differentiate between them.

For us, the option of changing the company after the ticket has been created would be sufficient.

One other possible solution would be to allow a pre-process email filter to change the 'from' address but keeping the reply to address intact. One could then have the user supply a tag in the subject to specify which client he was working for.

I have a work -around for this issue. But it is not pretty.

I needed to remove all references to companies and reference what company it is for when I am editing the ticket and adding a custom field.

Still need to work out the reporting aspect, but having this functionality would certainly be a good thing.

Since the email address is our unique identifier, there's no way to do what is being asked. Leaving open for workaround posted.

Migrated this feature request to the Cerb4 project. It shouldn't be too difficult, technically, to associate an address with two organizations. However it adds significant complexity to the interface.

http://www.cerb4.com/forums/showthread.php?p=1146#post1146

Implemented in 5.2