Has anyone tried to really "mass" email candidates?

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We are in the process of "recreating" all requisitions in an attempt to clean out the database and avoid "too many cooks in the kitchen" when it comes to recruiting. Many of our offices have created more than necessary requisitions, leaving our candidates scattered. We are also looking into doing a purge, so we want to mass email candidates from the database to ask them to reapply on our Careers Website if they have not been interviewed or hired. I've only had test subjects of up to maybe 10. Has anyone tried more? Thoughts or suggestions for this project are