When you send an email message, your email program sends the message to a mail server somewhere on the internet. To keep just anyone from sending mail through that server (i.e. a spammer), Internet Service Providers (ISP’s) have started being more particular about who is allowed mail through their servers.
These days, most mail servers require some type of authentication before allowing you to send a message. Think of it as if someone put a combination lock on the mailbox at the corner. To place a letter in the box, you need the right code before you can slip your letter through the slot. If the junk mail senders don’t have the code, their mail won’t get sent.
Traveling users often find managing outgoing mail troublesome. It’s not uncommon for a user to be able to send mail from their home location only to travel to a new location and find that they can’t send mail. Why does this happen?
There are 2 common issues which arise in this scenario:
1. Many ISP’s allow you to send mail through their server, but only when you’re connected to their network. For example, let’s say you use AT&T’s DSL at your home office. Without doing anything, AT&T will let you send mail from home, no problem.
But let’s say you grab your laptop and go to a friend’s house who uses Comcast. If you try to send mail from that different internet connection (where your machine has a non-AT&T IP address), AT&T’s mail server won’t accept your mail because you’re not on their network anymore. To AT&T, you look like you could be a spammer so they block your outgoing message.
To fix this, all you need to do is tell your email program to authenticate you by sending authentication; in this example your AT&T username and password with your email. This is known as ‘SMTP Authentication’ and must be enabled in your email program if you plan to send mail when you travel to a location which uses a different ISP. In Apple’s Mail program authentication is enabled here: Mail > Preferences > Accounts > Outgoing Mail Server (SMTP) pop-up menu > “Edit Server List” > Advanced:
Without getting too technical, each software process on a computer (email, web, instant messaging, etc.) speaks on a different ‘port’. When you send email, the default is to send on port 25. Many ISP’s (AT&T and Comcast included) have begun blocking outgoing mail on port 25 as a method of dealing with spam, particularly in the form of Windows viruses which use port 25 to replicate themselves. In our example, you can send on port 25 to AT&T’s server, but NOT to any other mail server on the internet. Read that again – it’s important to understand that some ISP’s only allow you to send mail to their server on port 25 and not any other. So back to your friend’s problem…
If your friend wants to send mail to Comcast’s server from your house, throughAT&T’s network, she would need to tell her mail program to use a different port when sending mail. It’s a sneaky trick – essentially she’s telling her email program if one door is locked, knock on a different door!
As a general rule, try port 587. You may have noticed the “Port” fields in the Apple Mail and Entourage screens above. This is where you configure what port to use when sending mail.
If guessing port 587 doesn’t work, contact your ISP and tell them that you need to send mail to their mail server on a port other than 25. They may provide you with a completely different SMTP server address as well as the right port number. For example, to send mail to Earthlink’s mail server on port 25 you’d configure the SMTP server in your email program to mail.earthink.net. But to send on port 587, you need to change the server address to smtpauth.earthlink.net and the port to 587. The upshot is that your friend may need to contact her ISP or the server administrator for the server she’s trying to send through to get the right settings.
One more thing – AT&T (and I’d think other ISP’s who block port 25) will unblock port 25 on your connection if you ask them to. All that’s usually needed is a call to their support folks and kindly ask them to stop blocking port 25 on your connection. Note: you’ll need your account number, username/password, or something to prove you’re the owner of the connection before they’ll do this for you.
What about SSL? Many AT&T/SBCglobal customers have begun receiving email from AT&T, requesting that they change the settings in their email program for security reasons. What this means is that AT&T wants to encrypt your email while traveling to/from their servers (*see note below).
The instructions they provide usually include details for turning on SSL encryption and which ports to use (usually port 995 for receiving and port 465 for sending). These settings should cause no problems, as long as you have your username and password settings correct.
I know some of this sounds like complete technobabble, but I travel to several different networks on a daily basis and using port 587 and SMTP authentication to send mail has completely eliminated any trouble with sending mail, from anywhere. Once you get the settings dialed in, you won’t have to touch them again. Whew!
Please feel free to contact me for more information about any of the information above.
Kirk van Druten – LANsharks Consulting
About the Author:
Kirk van Druten is the owner and founder of LANsharks Consulting, an Apple Macintosh network and consulting firm, serving Northern California clients since 1994.
*Nevermind the fact that once your email has been sent securely to their server, it may travel unencrypted across the public internet to your ISP’s server and then on to you. If AT&T wants to encrypt from you to their server, what the heck…