Symptoms

1. You set up e-mail notifications to Gmail.
2. Sending e-mail notifications fails with:
   Authentication failed

Solution

1. In your Gmail settings turn on Access for less secure apps:
   
2. In Acronis True Image settings specify in this order:
   1. SMTP server: smtp.gmail.com
   2. Encryption: TLS
   3. Port: 587

   It is important to select the encryption type first, and then specify the port.

3. In the SMTP authentication section specify your Gmail e-mail address and password.
   

E-mail notifications should be sent successfully.