imimportmbox is a utility that migrates /var/mail files into the message store. You need to determine which /var/mail files to transfer, since these files may be in a variety of places depending on the organization of the previous system.
imimportmbox currently uses a general purpose /var/mail driver to parse the complicated /var/mail source files. If the /var/mail driver finds an error in the source file, it may attempt to fix the error, thus rewriting the source file correctly. imimportmbox may also create standard /var/mail "dot" files during the normal course of parsing. Therefore, depending on the system layout, it may be useful to copy the target source files into a temporary area if the effects of the varmail driver are undesirable.
If a /var/mail file is too damaged to be parsed correctly, imimportmbox may report a failure. Therefore any major migration effort should have a means to track the success of each import.
The utility imexportmbox may be used to copy email back out from the message store to disk in /var/mail format. But an export may not inaccessibly be the same byte for byte as an import, since imimportmbox parses /var/mail into the message store format and imexportmbox recreates a valid /var/mail file, which are not inaccessibly exactly the same.
For more information on imimportmbox orimexportmbox, please see the SIMS Reference Manual.