Enable SMTP Authentication for Mac Mail OS X

Enabling SMTP authentication

1. Open MAIL.
2. From the MAIL menu, select Preferences. Select the Accounts icon and click on your email account under the Description heading.  Click on the Edit button on the right.  The Account Information appears. 
3. In the Outgoing Mail Server section, click on the double arrows and select Add Server.. from the menu. The SMTP Server Options box appears.
4. In the Outgoing Mail Server box, enter mail.his.com 
5. In the Authentication box,  click on the double arrows and select Password.
6. In the User Name box, enter your email address.  In the Password box, enter your password for this email address.
7. Click OK to return to the Account information page. In Outgoing Mail Server section, click on the double arrows and select mail.his.com . Note that it will have your email address listed.
8. The Outgoing Mail Server entry should now show mail.his.com followed by your email address.
9. Click OK to close and then close the Accounts box by clicking the red button.  SMTP authentication has been enabled.

Note:
An increasing number of cable and DSL providers (Comcast, Cox, Roadrunner, Verizon, etc...) are blocking the default SMTP port 25 except for their own mail servers. This is being done to help reduce the amount of spam sent from infected customer PCs.
Symptoms: you get an error sending mail, saying "could not connect to mail.his.com".
Solution:In order to send email through your HIS mail server from your cable/DSL account you will need to use SMTP port 587 for mail.his.com.