port 25 blocked ?
It's possible that if your server is at home, your ISP is blocking your port 25.
Which means that you can only send e-mail using the SMTP-server of your own ISP-provider. Like here in the Netherlands, most ISP's do so.
The reason is an anti-SPAM policy.
I do not say that it is your problem, but please check this out, it is good to know.