Mail doesn't get blocked because of the mail server you are using, but rather what you are sending and who you are sending it to. If you/your clients send spam mail (unsolicited emails) then no matter what you use, you'll get blocked. Even if you use Google/Yahoo or anyone else's services, you'll get your account suspended if you send spam. You can setup your own mailserver but make sure you have relays turned off so others can't use your mailserver to send unsolicited emails.