Releasing sending email after backup

Personal goodnight, I wonder of you, what needs to be done, so that the Proxmox send me emails when you finish backing up VMs? I ask this because I'm a Proxmox configured with a valid IP and even send emails normally, however I have some behind the same NAT and do not send emails (or not enough).
I wonder if you need a redirection on port 25 or What?

Thank you very much for help.