Question

Given that the destination settings only allows selecting either email or advertisingID as external IDs, can I use ID Sync to send both as external IDs to Google Ads Remarketing Lists? 

Product

Twilio Segment

Environment 

Segment Console

Answer

No, ID Sync can not be used to send both identifiers as external IDs, as the ID methods are mutually exclusive.

These IDs are processed differently based on the external ID that is configured in the destination settings. ID Sync would not work if wanted to be used to send both IDs at the same time, as only the configured one will be treated correctly as an external ID by the destination, which means it will be sent in the user_identifiers[] object, while the ID used via ID sync would go to user_attribute object instead, as a regular trait. 

Just for reference, you can go over these 2 objects in Google docs.

Additional Information 

Due to Google’s restrictions on identifier limits per request, the Google Ads Remarketing Lists destination can only include one additional identifier in audience payloads. 

For more information, refer to Google Ads Remarketing documentation and Google's public documentation on the UserData Object.