If you want to block mail from certain domains, eg *.ru or *.cn, then you can create 'rules' in VPOP3 to do this for you.
Where and how you create the rules depends on how VPOP3 receives mail and on exactly what you want to do.
VPOP3 Spamfilter
If you use the VPOP3 Spamfilter and want the spamfilter to quarantine the message, you can add something like this to the spamrules_userchecks.txt file in the VPOP3 directory:
DefineRule "MyRule" 1 "My spam rules" BulkScan Score [MyRule] From /\.ru(>|$)/i 100 From /\.cn(>|$)/i 100 From /\.com\.mx(>|$)/i 100 EndBulkScan
Incoming SMTP feed
If you receive your incoming mail using an SMTP feed to VPOP3, then you need to create an SMTP Rules: Go to Services -> SMTP Server -> Filtering -> Edit SMTP Rules, and create a new Rule to 'reject' the message if the MAIL FROM ends with any of the domain endings you don't want.
POP3 Download
If you receive your incoming mail by VPOP3 downloading from a remote POP3 mailbox, then you need to create Download Rules: Go to Mail Connectors -> (edit the Mail Collector) -> POP3 General -> Edit Download Rules, and create a new Rule to 'ignore' the message if the 'From' ends with any of the domain endings you don't want