Mac Mail: Set up trust for the SSL certificate

When connecting to an HIS mail server with SSL enabled, MacMail will issue a warning because the certificate's domain name (*.his.com) won't match your mail server's domain name. (The infamous Certificate Domain Mismatch Error.)
To fix this problem, you can tell Mail to ignore the discrepancy. Here are 3 methods to do so:

Method 1

• Quit your Mail app
• Open Keychain Access
• Locate the certificate in the keychain (search for "his")
• Find the *.mail.his.com certificate.
• Double-click the certificate
• Expand the "Trust" settings
• Change the "When using this certificate" option to "Always Trust"
• Quit Keychain Access
• Launch Mail

Method 2

• Quit your Mail app
• Open Keychain Access
• Locate the certificate in the keychain (search for "his")
• Find the *.mail.his.com' certificate.
• Right-click that certificate and delete it.
• Launch Mail
• Try sending an email. You should get a message from Mail saying "Mail can't verify the identity of...".
• Click "Show Certificate"
• Check the box marked "Always trust *.mail.his.com"
• Click "Connect"

Method 3

• Open the Mail app
• Go to Mail -> Preferences...
  • From the "Outgoing Mail Server(SMTP)" drop-down, select the "Edit Server List..." option.
• Select the proper outgoing mail server, then click on the subtract(-) button in the bottom-left corner to delete those outgoing mail settings
• Click on the add (+) button to re-add the outgoing mail setting.
• Enter "Description" and "Server Name:", then click on the Advanced tab.
• Select: Use the default ports(25, 465, 587)
• Use Secure Socket Layer (SSL) should be checked.
• At this point you will get a message from Mail saying "Mail can't verify the identity of...".
• Click "Show Certificate"
• Check the box marked "Always trust *.mail.his.com"
• Click "Connect"
• Back to the settings, "Authentication" should be set to "Password". The username is your full email address.
• Save your changes, then try to send a test email.