What? E-mail has both an inbox and a Sent folder. Searches can be done on each.
This is false.
In addition to the local copy, received emails are also retained and archived on your incoming email server, and sent emails are retained and archived on the email servers of the recipients. There are almost certainly local email copies of the various correspondents as well.
Unless deleted from all desktops, all servers, and all archives these mails still exist. The IRS is simply lying.