DN: Is it possible for the fellow to start their working contract at the secondment place, even if they are recruited by a beneficiary which will deliver the PhD diploma, and which will host them after the secondment?

If it is relevant to the project to start with the secondment, then it can be done.

However, it is not advisable to start at the secondment place, because there is a lot of introductory information that the recruiting beneficiary is responsible for. The researcher needs to know their main supervisor, they should know about their contract and the terms they are employed under in general.

The mobility rule would be counted for the place where the fellow is recruited (the recruiting beneficiary country), the starting date of the contract being the reference date.