You set up e-mail notifications to Yahoo or to Outlook/Live/Hotmail in Windows version of Acronis True Image.
Sending e-mail notifications fails with error message "An unknown error has occurred" or "Authentication failed".
Solution
Method 1. Fix email notification settings
Method 2. Enable account-wide email notifications
With this method, third-party email servers will be used only to receive email notifications from Acronis. All the sending part will be handled by Acronis servers automatically.
By using this method you will change email notification settings for all of your backup tasks on all the computers, where Acronis True Image is installed and your Acronis account is used.
Step 1. Disable email notifications under backup options for a particular backup task.