For existing customer information in another database, the short answer is *don't* import.
No, really. Just use a different backend and interface with it.
http://doc.otrs.org/3.0/en/html/custome ... backend-db
OPTIONAL: I'd suggest making sure (?) that the customer information is read-only on otrs, but if you want otrs to modify, just be aware that it *can* do that, and therefore affects both front-ends (not damage, mind you, but if you change a name or a login on one side, it will affect the other side, for good or bad.)
OPTION 2:
IMPORT TO OTRS database.
WARNING if you're using a different backend than otrs, and the backend is not readonly, this will add customers to the default Customer backend (maybe ldap, maybe to your CRM. Be smart about this!)
WARNING
If you want to mass import to OTRS, there is an opt/bin/otrs.AddCustomerUser.pl that can be used:
otrs.AddCustomerUser.pl [-f firstname] [-l lastname] [-p password] [-g groupname] [-e email] username
if you define -g with a valid group name then the user will be added that group
So if you use excel, for instance, you can make a batch by copy/paste into a column: (-g group is optional. If you don't have customergroup support enabled, it's not really relevant)
="bin/otrs.AddCustomerUser.pl -f " &
firstnamecell & " -l " &
lastnamecell & " -p " &
passwordcell & " -e " &
emailcell & " " &
usernamecell
then you should be able to copy this new column to a command line (in your otrs root, like /opt/otrs) and populate your database.
Please be smart about what you're doing. Backup your database before import. Test a small section before rolling out the whole thing. Make sure it works how you want. Be careful about conflicts of existing usernames. Those cell locations will vary relevant to your data, so if you copy verbatim, it's not going to work correctly until you make appropriate changes.
Standard disclaimer must apply: What I'm suggesting is something that should work based upon what exists in otrs already. I do not suggest you run this twice, though CustomerUserAdd will error with User already exists, if it can detect it. Make sure you know where the data is going to go.