Gmail email client categorizes received newsletters into their own tabs. Messages categorized as primary are seen at a glance as opposed to the other categories which are on their own tabs. There are five tabs:
Person-to-person conversations and messages that don't appear in other tabs
Messages from social networks, media-sharing sites, online dating services, and other social websites
Marketing, interests, social and political causes, and other promotional emails
Personal, auto-generated updates including confirmations, receipts, bills, and statements
Messages from online groups, discussion boards, and mailing lists
The email client user can categorize the emails they receive and influence which emails are displayed in the primary view. For example, a message that has gone to Promotions can be dragged to the Primary view. After this, Gmail suggests marking this sender as primary which will result in the emails from this sender going to the primary inbox in the future.
While Gmail and the email recipient are the only ones that can influence the categorization, the newsletter sender can remind the recipients that utilize Gmail to mark the sender's messages as primary to increase the attention paid to them.