Did you read the Net::Pop3 documentation? It says:

login ( [ USER , PASS ] )
...
Returns the number of messages in the mailbox. However if there are no messages on the server the string `"0E0"' will be returned. This is will give a true value in a boolean context, but zero in a numeric context.

If there was an error authenticating the user then *undef* will be returned.

So that suggests that you shouldn't be having the problem you claim and that you can also use defined if you like.

        - tye (but my friends call me "Tye")