According to a pair of new studies, efforts to comply with the European Union’s new GDPR regulations are leading to huge attrition in existing email lists. Many companies with email lists are asking recipients to opt back in as they update their privacy policies. But, according to CNBC, the digital marketing agency Huge found that 38% of Americans are ignoring those emails outright, and 23% are using them as a chance to unsubscribe from email lists. Another marketing firm, PostUp, estimates that only 15% to 20% of Americans are even opening the emails — lower than the already-dismal 25% to 30% open rate for the emails worldwide.

That has huge implications, because most data shows that email marketing is much more effective than display ads, social media campaigns, or even physical direct mail. Large email lists are considered business assets potentially worth tens of millions of dollars — value that is likely being lost as new rules shrink email lists.

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The European Union’s new General Data Protection Regulation, or GDPR, went into effect on May 25. GPDR establishes higher standards for what is considered “consent” to receive marketing emails, especially for recipients who aren’t already customers, and it applies to interactions with EU residents and citizens.

But rather than try to micro-target those audiences and risk potentially huge fines, many digital operations — including giants like Facebook — are simply implementing the same policies worldwide. That’s why even many Americans are receiving requests that they re-enroll in many email lists.

The effects can be truly devastating for companies — one marketing firm told CNBC that its clients have lost up to 80% of contacts. That may motivate companies to go the extra mile and maintain separate EU and non-EU lists. This could wind up being a one-time dip, though, as new subscribers click through the new opt-in messaging with as little attention as we’ve ever given to online privacy warnings.