[Dovecot] problem with IMAP authentication with Thunderbird in local network

[Marco Ceccarelli - tnx.it]

I've installed dovecot in our debian and when i login from localhost it work.
when we try from our local network it give an error as this:

Mar 31 11:25:27 linux2 dovecot: auth(default): client out:
FAIL^I1^Iuser=mcecccarelli
Mar 31 11:25:27 linux2 dovecot: auth(default): client in:
AUTH^I2^IPLAIN^Iservice=IMAP^Ilip=192.168.0.105^Irip=192.168.0.115^Iresp=AG1jZWNjY2ZWxsaQBzZW5uYTk0
Mar 31 11:25:29 linux2 dovecot: auth(default):
pam(mcecccarelli,192.168.0.115): pam_authenticate() failed: User not known to
the underlying ahentication module
Mar 31 11:25:31 linux2 dovecot: auth(default): client out:
FAIL^I2^Iuser=mcecccarelli

i see that whe i try to login from localhost it try with pam(mcecccarelli)
when i try from local network it try with pam(mcecccarelli,192.168.0.115)

what i have to configure to make authorized all ip from local network ?