Any successful and failed attempts to access an Egress email are audited. 
These audit logs are never deleted and can be accessed via: 

• The Sent Packages button within Outlook (you must have the Egress add-in enabled to use this feature)

•  Within the Sent Packages area in your Egress Administration Panel 

Once you have accessed the audit log, click the appropriate package. The 'Package properties' will open and you can select the Audit Events tab to show any successful and failed attempts to access the package.