Why can’t we send emails through the server? Is SMTP blocked

Most of the large ISP's now are requiring that messages be sent through the ISP's mail system to reduce the amount of spam originating from their networks. You can test this by doing the following.

go to start, run
type
telnet mail.yourdomainname.com 25

(substituting yourdomainname.com for your actual domain name)

press enter
You should see a telnet window that returns
telnet mail.yourdomainname.com 25
Trying 65.39.254.10...
Connected to mail.yourdomainname.com.
Escape character is '^]'.
220 mail.plhosting.com ESMTP
If you see anything other than
220 mail.plhosting.com ESMTP

then you must use your ISP's mail server for outgoing smtp as Your ISP is blocking connections on port 25 to our mail system.