Deliverability improvement help?

We do have quite a few deliverability recommendations here:

• https://customer.io/docs/journeys/email-deliverability-best-practices/
• https://customer.io/docs/journeys/deliverability-quick-guide/

You should also consider using our Transactional API to send your transactional messages so that they are separated from your marketing traffic.

One suggestion we have to try and maintain the best possible chance of deliverability of your transactional messages is to:

1. Separate your sending domains. Send transactional messages on their own sending domain and try your best to maintain best deliverability practices and a healthy domain reputation.
2. Configure your services to send API calls to our Transactional API.
3. Once you have a separate subdomain for your Transactional Messages and have setup sending via the Transactional API, you can apply to add the transactional subdomain to our Transactional IP pool.

Finally, if you haven't already, you should check out your sending domain's reputation using Google's Postmaster tools. You would prefix your sending domains with cio12345. (e.g. cio12345.example.com). That service will help you see how well you are doing in maintaining a good reputation, which is critical when it comes to avoiding placement in the spam folder.