Enable SMTP Authentication for Mac Mail OS X

For email accounts hosted on one of our Zimbra Email servers:
Confirm the name of the Plesk server: It should have been sent to you when the account was set up.
Your webmail address looks like: https://zmail.his.com:8443: use zmail.his.com as mail host name.

1- Open the Mail app on your Mac.
2- Choose Mail > Settings ( or Preferences in older iOS)
3- Select Accounts and choose your e-mail account.
3- Click Server Settings, Scroll down to the "Outgoing Mail Server" section
4- SMTP Server Settings should be:
Description: zmail.his.com
User Name: your whole email address.
Password: Your current email password
Host Name: zmail.his.com
Uncheck Automatically manage connection settings: Uncheck
Port: enter 587 (or 465 if 587 does not work).
Check Use SSL/TLS.
5- Click OK.
6- You have now setup the zmail.his.com HIS outgoing mail server.
Make sure that 'zmail.his.com' is selected in the drop-down menu next to 'Outgoing Mail Server'
7- Click 'Save' to keep the changes.

If the changes do not take right-away:
8- Restart Mac Mail: Close it and re-open it so It will use the new settings.