The following discovered partners exceeded the number of internal users they are allowed to contact. No more than %1 users ...

The following discovered partners exceeded the number of internal users they are allowed to contact.

No more than %1 users can be contacted by each discovered partner.
%2
Cause: Federated partners that were discovered through DNS SRV have attempted to contact more usernames within your enterprise than is allowed. Such a partner might be a legitimate peer with extensive connections to your organization, but it is more likely to be an attacker.
Resolution:
It is recommended that connections from these partners be blocked at the firewall. If a given partner is a legitimate peer then add the partner's domains to the allowed list.