Mac OS iPhone, iPad

1. When you see the "Cannot Verify Server Identify" message, tap "Details"

2. Tap "Trust"

3. If this does not work, edit the account: Settings -> Passwords & Accounts -> Select Mail Account -> Account

4. Change the incoming and outgoing mail server host name to:* 

*Please confirm with us your mail server domain if still not working

Mac OS Desktop

1. Click "Mail" menu then "Accounts"

2. Select the account and click "Advanced"

3. Update incoming and outgoing mail servers to:

4. Click OK

5. Restart Mac Mail, Mail -> Quit Mail, Start Mail