The error received is being caused because the Email server is rejecting the Username and password that is defined in GoldMine for the POP3 (Getting Email) setting.
Please review and adjust the POP3 Email setting for the specific user in GoldMine
- Log into GoldMine as the affected user
- Tools > Options > Email tab
- Accounts Tab
- Edit the affected Account(s)
- Set the correct Username and password for the POP3 (Getting Mail) server