SMTP Authentication means that your mail client must provide your login credentials every time you send an E-Mail. Usually, your client stores your password internally, so you are not required to type it in every time. Historically, the Internet was a more friendly place, and all mail servers allowed mail to be sent through them (also known as relaying) without any checking of who was sending the message. This resulted in large amounts of spam and unwanted mail being relayed through otherwise legitimate mail servers. In addition to increasing spam volume and server load, it was very easy to forge E-mail that looked to be fully legitimate, which led to many security compromises. By adding an additional layer of security (SMTP authentication) to your email accounts, only users that know the username and password for one of your accounts can send mail through your mail servers. In addition, since SeattleServer.com supports Sender Policy Framework, remote mail servers may verify that mail sent from you is really legitimate, thereby reducing the chances of your mail being filtered as spam.
Q. Okay, that sounds great, but it sounds kind of complicated. Do I have to do any extra work?
A. No, the only thing you need to do is ensure your mail client is setup as described in our guides to use SMTP authentication. Without it, you won't be able to send mail.
Q. My ISP blocks port 25, and tells me I should only use smtp.theirserver.com to send mail. What should I do?
A. Configure your mail client to use your SeattleServer.com-hosted SMTP server as shown in the guides, but change the port from 25 to 587. Port 25 was historically used for both sending mail directly to a final mail server or relay, as well as for authenticated E-mail. ISPs blocking port 25 keeps spammers and viruses from sending mail directly to targeted mail servers, so it is now recommended to use port 587 for mail submission, and blocking port 25 from untrusted hosts. In addition, sending mail through your ISP's mail server using any E-mail address besides the one your ISP provided violates Sender Policy Framework, so your mail will be identified as spam by many systems. If your ISP is blocking port 25, it is to reduce spammer abuse of their network. Using port 587 will work around the problem.
