Why cannot create a user with name user at mydomain.tld ?

[Ali Nebi]

Hi,

i have installed ispman and it is a frontend for cyrus-imap.

When i try to create a user, the ispman tries to create it in this format

user.user at mydomain.tld

and i get this error:

IMAP::Admin [ create ]: couldn't create user.user at domain.tld : try NO
Permission denied

Does cyrus allows to create a user in this format?

if i try to create it this way: user_mydomain_tld, then everything is ok.

Is there any workaround for this or i need to use something different  
than user.user at mydomain.tld?

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