You should check to see if the messages that are being sent contain any links that would be considered questionable/spammy. You can also try taking the content of one of the messages and checking it’s spam assassin score ( https://spamcheck.postmarkapp.com ). Source: over 2 years ago

Build a clean email that passes a spam check with flying colors (https://spamcheck.postmarkapp.com/) then use a warmup service like lemwarm, inboxally or neverspam as mentioned in the other comments. Source: almost 3 years ago

The issue sounds more email centric. You're likely hitting the Apache SpamAssassin limit on the remote email servers. Use https://spamcheck.postmarkapp.com/ to check the score of emails you've had declared spam, and follow recommendations to improve. Source: about 3 years ago

Have you considered using a tool to turn your Spreadsheet into API like restsheet.com, sheet2api.com, sheetson.com, or sheet.best? Source: about 1 year ago

Use a paid wrapper like sheet.best or sheety.co. Much easier and robust from my experience and the free plans might be enough anyways. Source: over 2 years ago

// Submit Handler Function SubmitHandler = e => { e.preventDefault(); console.log(this.state); http://axios.post('https://sheet.best/api/sheets/a6e67deb-2f00-43c3-89d3-b331341d53ed', this.state) .then(response => { console.log(response); }) }. - Source: dev.to / over 2 years ago