I have my own domain (on a dynamic IP) and run my own mail server but I use relay host to send mail through my ISP.
I recently got this bounce: (reason: 554 Service unavailable; Client host [my_isp's_mail_server_host_name] blocked using Barracuda Reputation; http://bbl.barracudacentral.com/q.cgi?ip=my_mail_server's_ip)
