To enable mail receivers to validate that your emails are legitimate, you have to add SIDF. SIDF are a merger between Microsoft’s caller ID and SPF (Sender Policy Framework). SIDF is implemented on the sender and the receiver side. On the sender side you have to add and maintain some DNS TXT records. On the receiver side you simply need an email server checking the stuff. The receiver does not use SIDF to do a pass/no-pass decision. Instead, the result is put into the normal spam detection algorithms. If you do not publish SIDF information, you should expect your mails to be ‘suspected’ more and more as SIDF becomes more widespread and as email administrators starts to squeeze the spam rules forcing SIDF to be required.
A good place to start is the www.microsoft.com/senderid site. I think this is a very good presentation, so start with it. Afterwards, you can use the Microsoft Sender ID Framework SPF Record Wizard to generate your SPF record.
If you add the stuff in Microsoft DNS, remember to select ‘Other new’ record type, Text (TXT) and leave the name field blank. This will result in a line in the GUI like –
(same as parent folder) Text (TXT) SPF data
You can check the SPF of my company with –
nslookup "-set type=txt" inceptio.dk
Go and declare your email domains!