Email Marketing Campaign

I have a Squarespace website. I have purchased my custom domain for my business through Squarespace. Additionally, I have subscribed to Google Workspace to manage my custom email addresses. Finally I have subscribed to email marketing through Squarespace, from which I set up a campaign and tried to send out test emails to view the marketing email. However, these test emails went straight into Spam for a yahoo email address and to Promotions folder for a gmail address (note: these two email address are owned by my husband and I to ensure that the test marketing emails made it to the Inbox). After talking to Google to help configure the DNS settings in Squarespace, the result was a hit or miss with the test marketing emails making it to the destined Inboxes. I am seeking help with either getting this email campaign to work (most if not all marketing emails making it into Inboxes) or for another option being set up/configured with a different marketing firm/website. The constraints are Squarespace as the domain host and website host. If required, Google Workspace can be replaced by another email provider as suggested or required.