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<div class="mail"><div class="mailhead"><span>TO: CUSTOMER</span><b>EMAIL</b></div><h3>YOUR NEXT PICK</h3><div class="slot"><div class="tile"></div><div><small>PRODUCT SLOT</small><strong id="offer">WELCOME SET</strong><span id="group">NEW CUSTOMER</span></div></div><footer>ONE TEMPLATE · TWO AUDIENCES</footer></div>

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const offer=document.querySelector('#offer'),group=document.querySelector('#group');let returning=false;setInterval(()=>{returning=!returning;offer.textContent=returning?'REFILL PICK':'WELCOME SET';group.textContent=returning?'RETURNING CUSTOMER':'NEW CUSTOMER'},3000);