Configure Microsoft Outlook Express with TLS and SMTP_AUTH. This is a common issue that can be overlooked by administrators for users who insist on using Outlook Express. The set up for secure login and sending email is not intuitive.
First you need to create the account, so choose Tools-Accounts-Add. The Display name is simply how it will look in the list.
Enter the full email address here.
Select IMAP for your mail server. This gives you a number of options in that you can access your mail in several different ways, web based or on your desktop. Your mail server must have a FQDN, Fully Qualified Domain Name, in other words three parts separated by periods, the hostname and the domain. If you do not know the mail server name find out before you continue. The outgoing mail server must also be listed and they are typically the same.
Provide an account name, again this will typically be the full email address, so this could be firstname.lastname@example.org. Enter your password if you want to have it check that automatically.
This will complete the first stage.
Once it is created, right click the account and choose properties. Now fill in the email address if not done so already.
Go the Server tab and be sure the incoming and outgoing mail is set. Also verify the email address and that you have the password set if you want it to be automatic.
At the bottom of the page you see the “Outgoing Mail Server”, check this box and select Settings. Your email account can be used to authenticate when you send email. This is the SMTP_AUTH, what this does is allows only people with email accounts on the server to send email. In other words, this is what stops spammers from using your mail server as a relay but allows you to send email.
Now go to the Advanced tab. Make sure your mail is going out on port 25 and you have selected the SSL option, as you see. Also, be sure to select 993 for incoming and SSL. What this does is provide encrypted communication between the user and your mail server.
That completes the Microsoft Outlook Express configuration. Now you can allow those Microsoft users to start enjoying the security and stability of Postfix.