i dont use for spamming. i use for connections. actually i just want 587 port open proxies. My system is like : client > proxy > MY SMTP SERVER > REMOTE SMTP SERVER. for that reason im searching just 587 port open proxies.Because my smtp server only allowing 5 connections per ip.
Try searching the marketplace for backconnect SOCKS proxies; usually port 587 and 25 are open for these services.