Really Good Email has more than 7k amazing email designs for you to use to stand out from others. They've email design for eCommerce platforms and fashion to brand email designs from Apple, Pinterest and many others. Do have a look at this resource here. - Source: dev.to / 22 days ago
Never tried but have a look at Mosaico and GrapesJS. Both are open-sourced and used by Mailtrain. - Source: Reddit / about 1 month ago
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