I used to have a problem with Roadrunner Internet.
I had no problems sending or receiving emails when in my providers Bright House's area. But when I traveled to networks outside Central Florida I couldn't send email through the SMTP at smtp-server.cfl.rr.com. That SMTP didn't allows foreign IP addresses to send out going email. So what I did was i used Googles SMTP server to send outgoing email. But when I set up the the server I had to use my Gmail account so eventhough it showed my gmail email address as the sender. Because I wanted the email account from roadrunner is my primary email i didn't like that. Well recently roadrunner has a mobil-smtp.cfl.rr.com that allows me to send emails outside of central florida. I would verify that you have the correct SMTP server name to send out going email.