GoogleApp jobs are not able to dredge mail. Found warning in RetainWorker log:
2015-09-02 10:55:33,145 WARN [RTWQuartzScheduler_Archive_Worker-7] com.gwava.gdata.GoogleIMAP: Connection failed with Oauth2Couldn't connect to host, port: imap.gmail.com, 993; timeout -1
Your firewall needs to have certain ports opened for Retain to connect to GoogleApps.
See: Ports Used by Retain
This article was originally published in the GWAVA knowledgebase as article ID 2608.