Recover Deleted Emails with exMerge Utility
If you are trying to collect emails deleted by a user at a business that uses a Microsoft Exchange Server for Outlook, consider asking the IT department to install MS exMerge utility (also known as Mailbox Merge Program) which can be used to extract emails from Exchange's Dumpster which may retain copies of emails after a user has deleted the email from his or her Deleted Items folder.
exMerge also has specialized searching capabilities when it is being used to extract emails from source storage to a collected storage file. Data selection criteria can modified to exclude duplicates of emails already in a target store or use the newly collected version to replace the version already in the target store. Specific folders can be selected for collection, and collection confined to emails in a particular date range. It's notable the date range can either be set for the time at which messages were delivered, or the last time they were modified - an important consideration in electronic discovery. If a user went over old emails during a relevant time period, you can make a strong argument that they are more likely to contain responsive information.
Targeted searches can also be run in the subject field description and attachment file names. You have a 'sub string match, ignore case' option which will run searches for any subject field or file name which contains part of multiple specified strings.