Hello @user2553 assuming your link in Newsletter is on your website where you can manage google tag manager, then you can set custom attribute or event that will be generated by google tag manager and synced to Intercom once they land on that URL.
https://www.intercom.com/help/en/articles/2631808-install-intercom-with-google-tag-manager
That attribute/event you can then use to target the relevant user with outbound Intercom message.
Alternatively, you can set Series with a purpose not to send any messages but to just tag user with a specific tag once they are on that URL. In the entry rules of the Series you will use Current URL = URL from the newsletter and then the next block, if they fulfill the entry rules would be tagging block.