Sending marketing emails on Shopify

Shopify provides its own email platform. Its free but has no automation so you'll have to send the emails manually... If you wish to have automation I would suggest using Klaviyo or Privy.

I use Klaviyo. For 2500 contacts per month I pay about $60 and it brings me at least 25% of my store revenues. For me it's a no brainer. They also have a basic free plan. See the pricing options here - https://www.klaviyo.com/pricing

Mailerlite is a great app and has a free plan for up to 1000 contacts.

I use Mailchimp as a marketing platform, it also has a free basic plan. You can easily integrate it with Shopify using shopsync. Here is how you do it - https://mailchimp.com/help/switch-shopify-shopsync/