I use dovecot, vpopmail.

I wish to restrict a mail user's login to its mailbox according to its ip address. I don't wish other users to be affected . Namely, for instance, abc@domain.com can login to its mailbox from a few specific ip addresses but the same user will not able to login from anywhere. Meanwhile normally other mail users can login to their mailboxes from all ip addresses. How can I do that with dovecot acl ? any advice.