Microsoft relies on various authentication filters to determine if an email is spam or not.
Common industry practices include reviewing email for the presence of a SPF Validation, Sender ID and DKIM records within email received.
The Sender ID Framework is an e-mail authentication technology protocol that helps address the problem of spoofing and phishing by verifying the domain name from which e-mail messages are sent.
SPF (sender policy framework) is essentially an extra DNS record that directly specifies where remote mail servers should be expecting to receive mail from.
DKIM (DomainKey Identified Mail) is a newer implementation of the older DomainKeys system, which is essentially a more complex approach toSPF/mail verification, that requires mail to be signed with a private key, and checked against a public key found in the DNS record. This essentially acts as a more secure version of SPF.
You can send an email from a email@example.com to firstname.lastname@example.org when sent, an email will return stating the verification of DKIM, DomainKeys, SPF, SpamAssassin, and Sender-ID.
However, in recent months, I have found that despite including these elements with emails sent out, Microsoft was still ditching legitimate emails. I found that once the recipient had our email address listed as a saved contact, they received our emails fine. So I’ve created a vCard for our company and urged our customers using Hotmail or Windows Live email services to save the vCard as a contact to ensure that our emails get delivered correctly.