Sending customized messages to guests

Hi all!

We are synched with Booking by iCal calendars, and for each reservation, our software sends a customized e-mail to the guest. We send that e-mail to the e-mail address that Booking inserts into the iCal, which is something similar to 7ea45cfassd19c0bcba6f536631016ef77@booking.com. However, we are noticing that since a few weeks the e-mails we send does not appear in the reservation messages and does not reach the guest either.

Do you know if there has been some change recently regarding this? any new setting we should activate in Booking? 

We would like to use the Booking API to communicate with the guest but the requests for accessing the Bookgin API are closed in the Connectivity Partner portal, so we have to deal with the iCals.

Thank you so much for your reply!