From SAP Hybris Marketing On Premise release 1508 onwards, it is technically possible to connect custom service providers (e.g. for email, text messages, messengers etc.) by implementing a custom provider adapter.
We created a series of documents that describe how this can be achieved in detail using a concrete example for developers. We use SendGrid as an example as it offers the possibility to request a test account for free. Thus, everyone should be able to repeat the described steps here and learn by doing.
We have splitted this example into three different documents that deal with different aspects of the connection and an appendix that contains the complete coding: