Microsoft have followed in Gmail's footsteps by moving their users promotional emails into a separate folder, away from their day-to-day personal emails.
Office 365 is mostly used for work purposes at businesses from one-man-bands to large corporates, so the impact is likely to be felt most by B2B marketers.
This great post by Email on Acid, a testing tool for email marketing designers, talks through the impact in more detail.
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