It is considered a security vulnerability by most ISP's. It is one thing we can do to proactively block SPAM.
Most ISPs block others from accessing their port 25. If you are currently attached to their network they will usually allow you to send E-mail through port 25 with no problems.
ie: Cox west will not let you send E-mail through their outgoing server when you are attached to the local coffee shop's internet who happens to be using Qwest. But when you go home and attach your computer to Cox West it works fine.
This is the first time I have seen an ISP block traffic to port 25 on another server.
Unfortunately because Cricket doesn't even offer E-mail you can't even configure your PC to send E-mail through their server.
They swore up and down they don't block port 25 but with the exact same settings I was able to send and receive E-mail through my companies ISP service. It was only a problem if I removed the ethernet cable and tried through Cricket Broadband. They are full of it and their so-called IT people know nothing.
To correct this problem for my client I had to sign them up for an account with yahoo bizmail and send E-Mail out through their SSL port 465.
It seems kind of silly but my client didn't want to change providers because of the price nor did he want to change his current Hosting company who only allows access to their outgoing mail servers through port 25.
