This article explains how to find out whether your ISP is blocking port 25 on your account. Port 25 blocking prevents any 3rd party outgoing mail servers from being accessed while connected to your ISP network via Dialup, DSL or Cable. Many ISP's (Internet Service Providers) are blocking what is called "Port 25" which is the port used to send e-mail. They have chosen to do this to cut down on the amount of "SPAM" mail that is sent. All e-mail sent via the Internet is routed through the port 25, the channel used for communication between a mail client and a mail server. eMail Verifier will be unable to fully test e-mail addresses, eMail Verifier can check the syntax of the e-mail addresses and whether the domain they belong to exists but the last step, connecting to the address MX Exchanger, can't be performed.
Unfortunately, there is nothing we can do to change this. The port #25 is the standard for sending messages and the one eMail Verifier uses. The only solution is switching to another ISP. Smaller local ISP's usually do not block Port 25. Note that if your ISP is Comcast you can update your account to a Business Class account with full access to port 25. In the case you are connected through AT&T or Verizon, port 25 can be unblocked at the request.
You can easily check whether you are affected by port blocking by using eMail Verifier itself, just verify a single address, an address from anyone but you, do no use any of your own addresses. Then go to the eMail Verifier console panel and look at the text returned by the server.
If port 25 is not blocked you will get a successful response with code '220' like this:
If port 25 is blocked you will get several connection retries followed by a timeout:
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