Suggestion: Email validation checker

Typo domains like these are a constant source of silent list decay. Two thoughts that might help in the meantime:

The cleanest fix is at the form level: a "did you mean gmail.com?" suggestion before submit (mailcheck.js-style). Since the subscriber confirms the correction themselves, the GDPR question never even arises. That's essentially what you're proposing as a native feature, and until Klaviyo builds it, it's doable on custom forms, admittedly not in the native form builder.

On the GDPR point itself: it may be less restrictive than you fear. Full disclosure, I work at an email marketing agency in Berlin. We recently did a bounce-list remediation for an enterprise client and wrote up the legal reasoning for their in-house counsel. The short version: correcting only the domain, and only where the entered domain factually does not exist (gmial.com, hotmail.con, gmail.de: Gmail only exists under .com, so nobody can own a mailbox there), is arguably not guessing a new address but rectifying an obviously inaccurate record. GDPR actually points in that direction: Art. 5(1)(d) requires accuracy, and Art. 16 gives a right to rectification. The safeguards matter though: we never touched the local part before the @, kept an exclusion list of real look-alike providers (email.de, mail.de, alice.de etc.), re-verified every corrected address against the receiving mail server, and kept the original in an audit column. Everything that failed re-verification was discarded. That approach recovered ~1,700 deliverable addresses in one project. Obligatory disclaimer: not legal advice, your DPO has the final say, and the ICO's reading may differ from a German DPA's.

If you want to dig into the reasoning, my boss Uwe-Michael Sinn wrote that assessment and is properly deep in this exact topic. Feel free to reach out to him on LinkedIn, he's happy to talk shop on it. On top of it he is Klaviyo Champion!

 https://www.linkedin.com/in/uwemichaelsinn/