How long should you keep email addresses?

An email address is personal data. Keeping it forever is neither permitted nor useful.

As long as the purpose exists

Somebody is subscribed to your newsletter: the purpose lasts as long as the subscription. After an unsubscribe that purpose is gone.

What you keep anyway

A suppression list of people who unsubscribed. That sounds contradictory, but it is exactly what stops you contacting them again by mistake. Keep the minimum in it.

Transactional data

Addresses tied to orders fall under your accounting obligations, not your marketing. Those are two different periods.

Inactives

An address that has not responded for years no longer has a real purpose. Deleting it is both compliant and good for your deliverability.

Write it down

Record the period and the reason. A retention policy nobody wrote does not exist at the moment somebody asks for it.