We're looking at the total donation amount raised for email messages using the Group Performance by Message report. The donation totals are clearly inaccurate as it is a lot less than what we expected.
The Group Performance by Message report will show how much money was raised by each recipient that is a member of the group. The report looks at the current membership of the group, not the membership at the time of delivery. If the donation totals are less than what was expected, then it's probably because the group membership has changed since the email was initially sent. The report is intended to look at current group memberships and how much money was raised across various email messages/campaigns. To see the total amount raised by an email message, the Donations by Email Message report should be used instead.