How to check in builder that one in the sequence has been replied by the customer

Hi Suraj, thanks for this great question. 

Currently, tracking or suppressing replies is not an available feature within the application. This is because Customer.io sends directly from the email address you choose, and any replies from your customers to that address never come back to Customer.io; their replies go directly to the address you sent from. That said, I definitely see how this would be useful and have submitted a feature request to our team on your behalf.

In the meantime, one thing we can suggest for tracking replies and/or measuring reply rates for your campaigns is to use specific 'reply-to' addresses in your campaigns (per message if you want to track on a per-email basis). For example, you could use an alias as your reply-to address so that the reply goes to any sort of tool you'd like it to go to and track replies there.

Unfortunately, I don't have a more specific recommendation right now since this is widely dependent on how the email address that is responded to is configured. For instance, if you control the mail server responsible for receiving at the reply-to address you could tap into it directly to monitor for responses and act on them accordingly.

In such a case, you could use Liquid to create the dynamic 'reply-to' addresses and then, once you know they've replied, send an event to Customer.io, which you could then use to trigger other campaigns in response to the reply.

If the mailbox isn't hosted somewhere you have access to then you'll need an alternate solution that lets you trigger the event based on replies. You could look into a service like Zapier for solutions that let you send requests to our API based on email replies. They offer triggers based on receiving an email at a Gmail (or G Suite) address or by using a custom address at their service. You can read more about this here: https://zapier.com/zapbook/email/

In the above example you could specify the Reply-To: field of your emails as a Zapier address and set it so that when responses are received Zapier forwards the message to any mailbox where you'd like a copy and also set it so that an event is recorded with Customer.io signifying that a reply was received.

Another difficult part of this type of integration is associating the email reply with a user ID in Customer.io. Each user in your account has a unique id attribute (set by you when they are created in your account) so you would need to send this unique value in any request to our API which would need to be retrieved on your end based on the email address that replied. We do offer a "/customers" endpoint in our Read API, which allows you to programmatically retrieve an ID by searching for an email address. That endpoint can be found here in our documentation: https://customer.io/docs/api/#apibeta-apicustomerscustomers_list

Note that this isn't a use-case we've fully developed into a best practice so ultimately if you do decide to implement this we'd love to hear more feedback on what you found possible and where there are limitations you've run into so we can better understand and develop an approach that works well.

If there are any changes to the product that help facilitate this type of user targeting based on email responses we'll be sure to make an announcement.

Please don't ever hesitate to reach out with any questions or concerns. Feedback like yours is invaluable to our team as we continue to create and update features for you and all of our users.