Outlook Port Assignment

I have changed companies and have tried to re-initiate Outlook using the new POP3 and SMTP servers. The POP3 works fine and I receive mail but I cannot send mail. I get an error message indicating the port assignment is the problem. I have verified that the port 25 is unblocked but I still cannot send mail. I contacted AOL (my ISP) and they seemed helpless unless I wanted to use their servers. Any suggestion on how to fix this other than changing ISP’s or dumping Outlook (not an option).