When making changes at Home > Tools & Settings > Server-Wide Mail Settings in Plesk Panel, following error occurs:
Error: DNS zone name is invalid.
Server-Wide Mail Settings > DNS zones for DNSBL service field contains an invalid sign/symbol.
DNS zones for DNSBL service must be separated by a semicolon ';' without a space.
Note: If spam protection based on DNSBL service is unchecked and contains an invalid sign, then the error may still occur.