While many marketers are collecting consumers’ personal information such as their name, location and birthday, most—70%—are not using that information to personalize their e-mails, according to a new report from e-mail services provider Experian CheetahMail.

That’s a missed opportunity because information such as a consumer’s gender (collected by 19% of marketers) or birthday (collected by 34%) can be used to send more targeted, relevant messages to e-mail subscribers, the report says.

“Your customers are offering you access to this personal information and expect you to use it to market to them as an individual,” the report says.

Marketers also have to pay heed to the changing ways that consumers are reading e-mails. 44% of e-mails are opened on mobile devices, which means marketers should take a mobile-friendly approach to e-mails by reducing the overall width of their e-mails to 560 to 580 pixels wide; increase the point size of all copy to at least 14 to 16 points; and space out calls to action so that they are at least 40 pixels apart.

The report suggests that marketers should regularly test their messages because small tweaks can produce significant results. For instance, when its clients have tested the impact of including symbols, such as hearts or stars, in an e-mail subject line, they’ve boosted their open rates up to 15%. Similarly, words such as “Pinterest,” “Pin us” or “Pin it” in subject lines have generated open rates that are 11% higher than their other messages and click-through rates 25% higher.

Despite Pinterest’s lure, only 32% of marketers display or promote their presence on the social network in their e-mails. That lags behind Facebook (highlighted by 98%), Twitter (91%) and YouTube (45%).

The report is based on an online Experian survey of 146 of its marketing clients.