[Dovecot] user name translation

i have the next question i like to authenticate users only by user ant not by user@domain

i'm using pam for authentication the users are stored bij first lette for name then back name

J.Hendriks     so no domain included.

bu i want them to login as J.Hendriks@domain  so i kan use the same user for more domains

in diverent mail folders b.v. mail_folder= home/%d/%u

but now pam is authenticating as user name J.Hendriks@domain   and not J.Hendriks.

is there a way to cut of @domain from name.

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