The PR DISPLAY TO parameter provides a list of display names (which may or may not include an address), not SMTP addresses, therefore there is no assurance that the email address will even be there.
On the Extended MAPI level (C++ or Delphi), you'd need to create a subrestriction (RES_SUBRESTRICTION) on PR_MESSAGE_RECIPIENTS that contains RES_CONTENT restriction on PR_EMAIL_ADDRESS / FL_SUBSTRING | FL_IGNORECASE.
If using Redemption (I am its author) is an option, it creates a recipient subrestriction if you specify Recipients (or To/CC/BCC) in a query:
set Session = CreateObject("Redemption.RDOSession")
Session.MAPIOBJECT = Application.Session.MAPIOBJECT
set olSentFldr = Session.GetDefaultFolder(olFolderSentMail)
emailStr = "John.Smith@gmail.com"
filter = "Recipients LIKE '%" & emailStr & "%'"
Set olSentFldrItems = olSentFldr.Items.Restrict(filter)