In case you are unable to send emails via Optimum Online that is also known as Opt Online, and you get the error message “cannot send outgoing mail due to port 25 is blocked” you should promptly call at Opt Online customer support helpline number and get the valid resolution. Also, you can follow these simple steps given below if you can’t send e-mail using Opt online or other ISPs:
Method 1. If you are unable to send emails and your ISP is blocking the port 25 you can use Port 587 that allow sending emails in some regions.
Method 2. You can also change your outgoing mail server to an SMTP mail server and easily can resume your services.