Why is Verizon blocking outbound port 25?
The majority of spam (unsolicited email) on the Internet is caused by malicious software viruses that take control of infected computers. These viruses direct the infected machines to send email through port 25. Verizon takes spam very seriously. Verizon blocks outgoing connections on port 25 to prevent infected computers from being used by spammers to send unsolicited email. Outbound port 25 blocking is a standard industry method to control spam.
For more information, click the link below:
Verizon | High Speed Internet - Your Attention Needed: Re-configure Your Email Settings to Send Email.