DuoMobile Implementation "issue"

I’m using DuoMobile and also a Windows-Domain, from where users are syncd with duo.
I also have passbolt. Now i connected Passbolt with Duo and found, that Passbolt somehow uses a “strange” user, to authenticate at Duo.
Let’s say i have a user “Max Muster” with mailaddress “muster@mydomain.com
In Duo the user is synced from AD with mmuster@local.domain and mailaddress “muster@mydomain.com
This user registered in Passbolt with his mailaddress. Now, when i try to use Duo, it says: error, your are not enrolled. When i look into Duo Admin Reports i can see, that Passbolt wants to authenticate “muster” as user, what is the part of the mailaddress before the @. So, this is not so good and leads to the problem, that in this way, i have to add another attribute to all my AD-Users, which contains the string of the mailaddresses before the @.
Can you please (or can i even do it on my own?) change this behavior, so that passbolt will use the whole mailaddress as user?