From the Finder desktop, double-click the Lexmark 3500-4500 Series folder.
Double-click the Lexmark 3500-4500 Series Center icon.
From the menu, choose Advanced 
Network Scan Access.
The Scan Network Access dialog appears.
Press + to search for printers connected to the local subnet.
The Network All-in-One Selection dialog appears.
In the search field, type the IP address of the print server. Consult your network administrator for help finding the IP address of the print server.
If you want to narrow your search to a certain subnet, type the IP address of the print server and the subnet mask in CIDR notation.
On your keyboard, press return.
From the Network All-in-One Selection dialog, select the printer you want to scan to your computer.
Click Select.
Repeat step 4 to step 8 for every printer that you want to scan to your computer.
When finished, click Done.