The moment you give someone an opportunity to create outbound connection to port 25 from your IP, you are certainly risking (well, guaranteeing) those IPs to be

The moment you give someone an opportunity to create outbound connection to port 25 from your IP, you are certainly risking (well, guaranteeing) those IPs to be listed at various blocklists. And you will be the one that will have to deal with abuse complaints.