Both Google and Yahoo! made announcements outlining new requirements for email senders. These include a requirements to :

• Authenticate your emails following well-established standards, most notably signing DKIM from your “from” domain.
• Additional authentication steps include the Sender Policy Framework (SPF) which enables the receiving mail server to verify whether or not tan email claiming to come from a specific domain is actully sent by an IP address authorized by the domain admin.
• Domain-based Messahe Authentication, Reporting & Conformance (DMARC) allows you to create rules to tell ISPs how email should be treated if SPF and DKIM fail or are not present.
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