Error: a Gmail to Gmail email via an Infomaniak address forward, fails to reach destination

If you send an email
from abc@gmail.com
to xyz@domaine.com (the domain you have at Infomaniak)
and that on this email address at Infomaniak you have a redirection to abc@gmail.com
then abc@gmail.com will never display your email.

The problem isn't that the redirection doesn't work: it's more a question of a particularity of Gmail: an email from Gmail to Gmail via the redirection of an address at Infomaniak will cause a problem on the side of Gmail, in the way it handles mail.

Your message will never arrive (because as far as it is concerned it is already in the box, in the items sent).