E-mail Notification Issue

We are on Unifier cloud and are on the verge of losing customers due to issue with Unifier e-mail notifications.

Some of our customers do not like to sign into Unifier but would like to review and comment through reports received with e-mail notifications once the task is assigned to them.

The issue is, sometimes the attachments to the e-mail are over the allowed limits of the customer e-mail system and those notifications are rejected. Now, Oracle e-mail system puts them in soft suppression list, so no further e-mail notifications are sent out to them. Since we have no visibility of this list, we are not aware that customer is not getting the notifications.