The University of Virginia has collated a timeline of requests and responses to multiple requests under Virginia FOIA. Since the full exchanges between requesters and the university are provided, it is a good way to see the issues that can arise.
First note, that while anything can be requested, the response depends on multiple issues - whether the records exist, whether they are 'public records', whether they fall under any exemptions in the FOIA law, and whether they are protected from disclosure under any other relevant laws (such as FERPA, which protects students personal information). Note that Virginia FOIA requires the requester to be a Virginia resident (which is why Chris Horner of CEI is now using ATI as a vehicle for these requests).
For any specific request, particularly for broad categories like 'all emails', it is not a priori obvious that a specific individual email that meets the search criteria is releasable. That generally needs to be decided on an email-by-email case. In response to Greenpeace (who requested records related to Pat Michaels), UVa rightly made it clear that no 'unfiltered' release of records would be possible.
Given then that extremely broad requests of emails will likely result in thousands of potentially responsive documents, someone needs to go through each of those records to assess the releasability. Federal and Virginia FOIA allow for the charging of fees to cover the cost of searching, redacting and reviewing documents, though this is sometimes waived in federal cases where agency staff are permanently assigned as FOIA support etc. Note that ATI initially challenged the application of fee for reviewing the documents, but UVa insisted that this was in fact permitted under guidelines from the VFOIA Advisory Council.
UVa therefore has requested deposits of fees prior to commencing any individual email review process, based on the reasonable estimate that one person can review roughly 90 emails an hour. (Other estimates from similar situations might give 70 to 100 emails/hour, but it depends clearly on the complexity of the material). UVa appears to be using law students to perform the reviews and are charging $25/hour for that. In cases referred to here, the number of documents is on the order of 35,000 individual records - implying eventual costs of review at $8000 or more (final costs to be decided once review is complete).
Issues: Fees, exemptions, standing