Okay, so after some investigation ( https://issues.apache.org/jira/browse/INFRA-12252), it appears that notifications@ is simply configured to block email from non apache addresses.
So, I have three possible solutions, if the Accumulo devs wish to receive build notifications from my instance of Jenkins: 1. I use my personal ASF creds on Jenkins to send build notifications as myself. 2. The Accumulo project request the configuration of notifications@ to be changed to allow non-apache addresses. 3. I configure Jenkins to post to the dev list (if possible). My preference in order is #3, then #2, then #1 last.
