The LEM does not have a native "digest" function to aggregate messages into hourly/daily packages. I agree with njoylif: If your rules are firing that many e-mails, you need better rules. A rule being triggered should be a call to action, and too many "calls to action" means the LEM is crying wolf a lot and it'll get easy to ignore the messages. Something you might consider is using the "Infer Alert" action in rules. This allows you to take some number of events and create your own event out of it, with custom information in any field (I like to put company names in the ProviderSID or ToolAlias field). Then you make an alerting rule for "If I see 10 events from ToolAlias = MyCompany, send an e-mail." It's sort of an event "gear reduction" to manage alerts.
Also, you can run reports on Inferred Alerts or on your custom data values to get your digest. If you create that search in nDepth and set it to run on a schedule and e-mail out, it could emulate the behavior you're after.