You can configure Duplie to automatically send out weekly (also bi-weekly or monthly) emails to your volunteers with upcoming sign up opportunities.  This is configured by logging in as an administrator and going to Site and Email & Engagement.  There you will see a tab named Auto Recruit.  There are various options you can choose when setting up your auto recruit schedule.

Duplie will try to no "blast" all your volunteers for minimal opportunities.  So if you have 1500 volunteers in your database and 3 openings for the upcoming week, the recruitment will notify them on a ratio you define.  For example, 10:1 will notify 10 volunteers for every 1 opening...  We do this so we aren't annoying.  Contact us at info@duplie.com with any questions.