In order to send e-mail messages (appointment confirmations) to customers from Plan-IT Online, Plan-IT Test Drive Web, and Plan-IT Workshop Web, Plan-IT must be added to the SPF record of the mail server. This notifies the mail server that Plan-IT has permission to send emails to customers on behalf of your organization.
To give Plan-IT this permission, add the following to the SPF record: include: spf.plan-it-online.com
For example:
v=spf1 include: spf.plan-it-online.com -all