Hello @Craig_Thonis
Thank you for your response.
The error was caused by the "contact date" we implemented in the native scheduler of our recurring deliveries because we wanted to take into consideration the pressure rules.
This is how the contact date was implemented

When we disabled the scheduler ( we opted for "No scheduling..."), there was no problem and all the emails went through.
Do you have an idea how we can resolve this, please? Because we still need the pressure rules to be taken into account.
Thanks
Best regards