Make sure a correct DNS address has been input into the network preferences under "Details". Contact your wireless network carrier for the address of their primary and secondary DNS servers.
If this still doesn't work, try replacing your email server's name in your email application software with the actual mail server's IP address. You can get these numbers from your ISP.
When attempting to send email, the error messages "Cannot Connect With SMTP Server" or "Unable To Send Message" appear.
Make sure your SMTP configuration settings are correct.
Your SMTP server may have Spam protection (blockage of unsolicited e-mails) or domain security, locking out your modem. Call your wireless carrier to find out if they have an alternative SMTP server available for your use.