After so many tries , so much time spent reading the docs and googling i decided to post here.

First, Lmtp was failing when verifying user cause it was not getting the domain.
So i i have put R=EnvToSMTP in /usr/share/sendmail-cf/mailer/cyrusv2.m4 instead of R=EnvToL/HdrToL.
From now on every time a mail is received i have something like :
"lmtpunix[]: verify_user(nsxxx.ovh.net!user.contact) failed: Mailbox does not exist. Whereas mail was sent to contact@racing.com not to contact@nsxxx.ovh.net !!
nsxxx.ovh.net is just the main host name.

I tried a lot of possibilities "define(`confBIND_OPTS',`-DNSRCH -DEFNAMES')" "FEATURE(always_add_domain)" "FEATURE(nocanonify)" without success. I always have this nsxxx.ovh.net host domain in the maillog verify_user part

I am using sendmail 8.14.2-4 on fedora core 9
+ cyrus imapd with pam auth.
I will post or link my config files on demand.

Im definately not a mail guru
Thank you in advance for your precious help.