Answer: It looks like your internet provider is blocking port 25. It is explained here: Why eMail Verifier loves port 25 so much. I recommend you to read that page as it explains the issue in detail and also offers possible solutions.
Maintain clean mailing lists checking the validity of recipient's e-mails addresses. eMail Verifier can save time and money for businesses who send newsletters to their clients, nonprofit organizations who send bulletins to their members, or any person or business that needs to maintain a clean e-mail contact list.
eMail Verifier is your powerful solution for the standard "message delivery error." Email Verifier verifies every e-mail address from a given mailing list, allowing you to determine 80-90% of "dead" email addresses.
eMail Verifier works on the same algorithm as ISP mail systems do. Addresses for e-mail are extracted from a Domain Naming Server (DNS) and eMail Verifier tries to connect with SMTP-servers and simulates the sending of a message.
It does not send the message though - eMail Verifier disconnects as soon as the mail server informs the program whether the address exists or not. Email Verifier is a very effective piece of software that can verify over 10 e-mails per second .
It can verify single e-mails or huge lists. (eMail Verifier is multithreaded, providing high speed verifying).