SMTP outbound blocked – AT&T Community Support

SMTP outbound blocked – AT&T Community Support

Re: SMTP outbound blocked

‎11-22-2010 10:07:53 PM

The port 25 outbound block really shouldn’t bug that many people. Using SMTPS (SSL/TLS) is FAR preferred.

For client-to-server communications, simply checking the box or dropdown or whatever in outlook to use SSL or TLS for SMTP would fix it handily if your mail server is setup to handle SMTPS on 465 or 587 – without the need to unblock port 25. So if that didn’t fix it either your server doesn’t accept SMTPS or you’ve got a bigger issue.

AT&T only blocks outbound 25, and a simple call or chat to tech support will unblock it for free. (My case was special as something with my account provisioning was goofed up – BUT the initial unblock of outbound port 25 worked and was handled quickly… and freely)

Just say, “I need port 25 outbound unblocked”.

Here’s how you can test…

(Forgive me, I’m not a windows guy, so this may not be exact)

First, since you’re running windows 7, install telnet.


Control Panel

Programs And Features

Turn Windows features on or off

Check Telnet Client

Hit OK

Then fire up a command window. Either powershell or cmd is fine. Hit windowskey+r for a run prompt and type in “cmd”, hit enter or OK. Should see the black command prompt box.

At the command line, type in “telnet 25”.

You should almost immeadiately get a blank screen… maybe a banner along the lines of “220 ESMTP…”. Typing ‘quit’ and hitting enter should return you to the normal C:\whatever prompt. Should be very quick.

If it just sits there with “trying 25…” for a long time and finally fails with connection timed out… then port 25 outbound is blocked.

Test against another mailserver as well. is a good test – it accepts SMTP via 25, 465, and 587.

You should also test telnet to 587 to your mailserver to ensure that works at least. If so… again… checking SSL for SMTP servers should work just fine. AND it’s far preferred to use SSL anyways!!!

Of course, disable any software firewall you have on your machine, and try again. The basic Windows firewall will mess with you as well I’d imagine – again, not a windows guy, but you can disable that thing too.

Don’t leave the firewall disabled. If that’s the problem – you need help configuring your software firewall, and I’m not the guy to help with that. I’m more of a server/network guy… don’t even use windows if I can help it. But I’m sure no matter what software firewall you’re using you can allow SMTP and SMTPS in it.

Anyway, testing that stuff lets you know where you stand. Testing beyond that gets pretty in-depth as you can see from my earlier posts. I went as far as doing packet captures on both ends and testing many many mailservers. But again… my problem was very abnormal.

via SMTP outbound blocked – AT&T Community Support.


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