Some Internet Service Providers(ISP) restrict the access to port 25 on their networks in an attempt to reduce the spam sent out from compromised computers.
If your ISP is restricting access to this port you will not be able to send e-mails using the default port. As an alternative, we have opened port 26 and 587 in order to circumvent the restriction. Regardless of what SMTP port you use, your e-mails will be sent in exactly the same way as such there won’t be any difference if you’re using 26 or 587.