Cannot send an invitation email to meeting participants

To reproduce:
Configure the email settings.
Create a new meeting “In preparation” and add a couple of participants
For those participants make sure the email address is added to their profile.
On the meeting page, below "Type here the message you want to send to the participants (optional) :", type a message and click "Send an invitation email to these users"

You get the following message: "An error occured while sending the notification emails." (see attached)