When e-mailing an authorize.txt file to email@example.com, a *.dat file is received from firstname.lastname@example.org.
For security purposes, e-mail servers, most commonly Microsoft Exchange, may convert attachments to *.dat files. This behavior is heavily dependent on the e-mail server configuration. See the e-mail server administrator for details.
Provided the conversion process has not corrupted the attachment, rename the *.dat file accordingly:
For licensing ArcGIS Desktop: *.respc
For licensing ArcGIS License Manager: *.resps
Double-click the authorization file to complete the authorization process.
If the ArcGIS License Manager is being authorized, use the workflow provided in the following knowledge base article, "HowTo: Authorize ArcGIS License Manager 10 Offline (by way of email or file upload)", to run through the authorization process a second time.