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tl;dr: Initially go slow and do a proper warm-up of your domain. Make sure hygiene points are taken care of like setting up DKIM, SPF, clean email list, etc. To start with depict human behaviour while doing outreach. Take help from friends, and colleagues to warm up your domain. Ask them to engage with your emails. Also you can use automation tool for warming up (but don’t rely only on it). Then check on your content. Basic pointers like email must not be image heavy etc.

Use this following tool to warmup your email https://www.gmass.co/warmup

Thank s@chintan bavishi and @Alok Gangrade So my product's domain is already warmed up and since it's a unicorn and already has 1000s of customers I don't think the domain is the problem here. is there any checklist I have to consider for the content? Like the one point suggested by Chintan here?