With Squarespace, you’re dealing with its appropriately-named ‘Squarespace Email Campaigns’ feature. This is more expensive than Wix’s Shoutouts, but does provide a bit more functionality, in that you can use it to create autoresponders (a series of messages that are automatically sent after a user takes an action — for example joining a mailing list or buying a product).

One thing to pay particular attention to with Squarespace Email Campaigns is that it only permits a double opt-in approach to subscription. Double opt-in means that in order to sign up to your mailing list, your site visitors not only have to enter their email address into a form, they have to click on a link in a confirmation email before they are subscribed. Whilst this can reduce the number of fake subscriptions, it can also significantly reduce sign-up rates.

Wix, by contrast, takes a single opt-in approach to subscription (although oddly, doesn’t facilitate double opt-in).

In terms of pricing, Squarespace’s Email Campaigns is considerably more expensive than Wix’s ShoutOuts feature; prices range from $7 to $68 per month, but with much more restrictive limits on how many e-newsletters you can send out per month. 

For example, a $7 Squarespace Email Campaigns plan limits you to sending 500 emails per month; the cap on the $68 plan is 250,000. The respective limits on Wix’s cheapest and top-tier plans are 9,500 and 1,000,000 respectively.

Ultimately if you’re looking for advanced email marketing functionality (split testing, marketing automation, CRM etc.) you are not going to get it with either Wix or Squarespace’s email marketing tools. 

And because of its lack of single-opt in functionality and its generally high pricing, I specifically advise against using Squarespace Email Campaigns.

However, if you are content with a simple and cost-effective way to send out occasional e-newsletters, then it’s hard to argue with Wix and its ShoutOuts feature.