[turba] Syntax of email address rejected

[Bruno Costacurta]

Hello,

using Turba (latest version 4.1.3) I can insert following email address:

john at mail.com

but not

john1234 at mail.com

which is reject with error message "john it not a valid email address".

I modified few months ago the file backends.local.php and  
attributes.local.php to add an additional email address.
Briefly, I simply added a new field.

Did I broke something ?
Where is the code of the syntax email address checking ?

Thanks for attention.

Bye,
Bruno