What's the difference between Pro and a group subscription?

Gaggle Mail Pro is a subscription bought by individual members of free groups, which gives them (and only them) access to paid features. Once someone has paid for Gaggle Mail Pro, they get access to paid features in all the free groups they're a member of.

Paid group subscriptions (Standard and Premium) are usually paid for by group administrators and give everyone in the group access to paid features. The features depend on the level of subscription they choose. See our Pricing page to compare Standard and Premium.