Local mail not deliverd OR hostname is setup improperly

[Snickers]

About 2/3 weeks ago, i've re-installed my DirectAdmin server, i moved from Debian to CentOS 5.4, at first everything looked fine however after a few days i received messages from my users that mail wasnt delivered...

but i was receiving mine... strange...

it turned out, only mails send to the local accounts (first account created) where not receiving emails.

after some looking around ive found that if i changed the hostname from:
server.domain.com to Server.domain.com (yes, only changed the S) local mail delivery was fine again... however now i;m receiving a daily e-mai:

Subject: This is e-mail notification to warn you that your hostname is setup improperly on your system.

if i change the hostname bcak to server.domain.com local mail stops again :s

what should i do?

thanks!

 

[scsi]

/usr/local/directadmin/scripts/hostname.sh <hostname>

 

[Snickers]

/usr/local/directadmin/scripts/hostname.sh <hostname>

if only life was that simple

/usr/local/directadmin/scripts/hostname.sh Server.domain.com
/etc/init.d/exim restart

(exim log) // mail admin
2011-04-08 22:51:41 1Q8Ieb-0001W4-A8 <= [email protected] U=root P=local S=349 T="test" from <[email protected]> for admin
2011-04-08 22:51:41 1Q8Ieb-0001W4-A8 ** [email protected] F=<[email protected]>: Unrouteable address


so.. back to /usr/local/directadmin/scripts/hostname.sh server.domain.com
and a exim restart

mail works fine again, however putting a
echo 'action=tally&value=all' >> /usr/local/directadmin/data/task.queue
(which triggers the e-mail)
New Message: This is e-mail notification to warn you that your hostname is setup improperly on your ...

sadly no luck