You receive multiple e-mail notifications for the same backup job when Altaro VM Backup is configured to send notifications to more than one recipient.
This behaviour indicates that your mail server is throwing back an error when trying to deliver the e-mail to one or more of the recipients in your list, thus Altaro will retry the message again to all recipients - hence the valid ones receiving multiple notifications.
Work by elimination to find the invalid recipient. The recipient(s) actually receiving multiple messages can be ruled out from any issues, so start with the recipients are NOT getting the e-mail notifications and check that their addresses are correct and that their mailboxes are able to receive e-mail messages. Also, try removing these recipients from the E-mail Notification settings in Altaro and test without them.
You can also check the response being given to Altaro by your mail server in the following log file:
Open this file in a text editor and from the bottom upwards search for the keyword: "Notifications.NotificationProvider"
Example log of a successful notification delivery:
27/04/2016 20:15:22.105 Altaro.Providers.Notifications.NotificationProvider: Notification Queued
27/04/2016 20:15:35.227 Altaro.Providers.Notifications.NotificationProvider: Sending Email - waiting for confirmation. ID: 680300466
27/04/2016 20:15:36.850 Altaro.Providers.Notifications.NotificationProvider: Email sent - confirmed. ID: 680300466
27/04/2016 00:45:01.562 Altaro.Providers.Notifications.NotificationProvider: Sending Email – waiting for confirmation. ID: 707101606
27/04/2016 00:45:03.909 Altaro.Providers.Notifications.NotificationProvider: Email sent – confirmed. ID: 707101606
27/04/2016 00:45:03.909 Altaro.Providers.Notifications.NotificationProvider: Insufficient system storage. The server response was: 4.5.3 Too many recipients