Information about "bounce rate too high" causes, the rate setting and resetting the notification
Mail list owners can change the notification setting at: Admin > Edit List Config > Bonces – Bounce Management. This setting defines the bounce rate (% of subscribers bouncing) required before the sever notifies the list owner bounces exceed the set values. The default values are: warn=30%, halt=50%. More info at: https://wiki.illinois.edu/wiki/display/maillists/1e.+Bounces
Resetting the Bounce Rate:
To reset the bounce the bounce rate go to: Admin > Bounces. Review the email list, select the checkbox next to the email address you want to “reset” or “delete” from the list.
See the screen shot below: