[exim] unable to authenticte (4.89 maybe conf error?)

On a new machine -debian 9- i have installed exim4,
it work except that trybg to connect from a mobile i get this result:
*this on port 465, 587 and 25, aster stattls do the same)

<<250 HELP
>> ehlo hostmaster.*.it
<<250-w Hello hostmaster.*.it [2001:*:*:*::33]
<<250-SIZE 52428800
<<250-8BITMIME
<<250-PIPELINING
<<250-PRDR
<<250 HELP
>>AUTH LOGIN
<<503 AUTH command used when not advertised

differently than another machine with apparently same configuration, and
working normally i get the PRDR line instead than the AUTH PLAIN one.
where I have to touch to eneble it ?


--
Leonardo Boselli
Dipartimento Ingegneria Civile e Ambientale UNIFI
tel +39 0552758808 +39 3488605348