I turned off the firewalls and tested - it went through. I have another firewall that had my other ip still flagged because it was on the rbl from before. I added it to the safe networks list, and all seems to be fully functioning again. I can't believe I didn't check the other firewall before - I only bothered with fail2ban and my configuration of main.cf because the issues started around the time I was messing with those.
Thanks - I appreciate your help, and all the work that has gone into ISPConfig. It's been a great help managing my sites.