Can 't SEND emails using OUTLOOK EXPRESS

When I try to send an email using Outlook Express, I get message, "the SMTP
Server returned an error. Account: ATT Worldnet E-Mail Server,
mailhost.worldnet.att.net, Protocol SMTP, Server Response 12.72.243.194 has
too many connections (2) on mtiwmhc 13, Port 25, Secure (SSL): No, Error
Number: 0x800ccc60.
Thanks for any help.
Dave