When sending an email from Exchange to Notes the email receives with a winmail.dat attachment
This is cause by the value set on the mAPIRecipient attribute for the contact object
Change the value to false to resolve this issue.
For more information on this please refer to following Microsoft Article:
Microsoft KB Article ID: 924240 - "The email message attached with winmail.dat when you send a mail from Exchange to Lotus Notes through a SMTP connector"
Microsoft KB Article ID: 2487954 - "An Office 365 admin wants to specify the email message format that's used for external recipients to prevent Winmail.dat attachments"