Own-Mailbox, the first 100% confidential mailbox
The reason for SMTP servers being better off in a proper data-center is not really due to port 25 being blocked at home, it's the entire infrastructure that assures reliability, so if your power goes out or your home router decides to die or your ISP is having issues, etc, you would start losing emails right away.<p>EDIT: I understand SMTPs are resilient but it also depends on the type of error they get back, even then it can't be expected that all servers keep retrying for long periods of time or even handle triple bounces. 
So you 'could' start losing emails right away, is a better way of saying it.