Hotmail Requires Sender ID

According to The Direct Marketing Association:

Microsoft will begin next week to notify its Hotmail customers when the Sender ID protocol is unable to verify the authenticity of an e-mail message. Messages that have not been authenticated will most likely be placed into a customer’s junk folder or deleted altogether in conjunction with other spam filters.

According to Microsoft, Sender ID works this way:

1. The sender transmits an e-mail message to the receiver.
2. The receiver’s inbound mail server receives the mail.
3. The inbound server checks which domain claims to have sent the message, and checks the DNS for the SPF record of that domain. The inbound server determines if the sending e-mail server’s IP address matches any of the IP addresses that are published in the SPF record.
4. If the IP addresses match, the mail is authenticated and delivered to the receiver. If the addresses do not match, the mail fails authentication and is not delivered.

If you want to checks the DNS for the SPF record of your domain, run DNS report.

Currently Hotmail does not reject mail if you do not have an SPF record. The message just receives icon.

Also, note, Sender ID is different from SPF and requires a different setup. See MS Sender ID for details.