How can I link received email replies to the original sent emails?

I use Advanced ETL Processor to send emails automatically and also to receive and process incoming emails.

When I receive an email, how can I determine whether it is a reply to a specific email that was previously sent by Advanced ETL Processor?

Please advise..

Every time an email is sent, it is assigned a unique Message-ID.
When the recipient replies, the original Message-ID is added to the reply’s In-Reply-To header.
This is how email replies are linked to the original message.
You can view these headers by opening the email’s source in a text editor.

Here is an example.Message-ID:
<LO2P265MB439827C451D09CA99994C973EABF2@LO2P265MB4398.banana.COM>
In-Reply-To:
<LO2P265MB43985687653B33365925E7CDEAD4A@LO2P265MB4398.london.COM>
Accept-Language: en-GB, en-US
Content-Language: en-GB
X-MS-Has-Attach: yes
X-MS-TNEF-Correlator:Right now the only way to extract this data is to write a script.

Better option is to tweak our software and store this information in variables.

Anyway thank you such an excellent and useful question. 

We will add variables for you and let you know once changes are ready

As promised, we have added the Message ID variable to the latest release. Support for the In-Reply-To header has not yet been implemented.

For now, you should start storing the outgoing email information, including the Message ID, in your database.

This will allow you to match and track replies once In-Reply-To support is available.