[CentOS] Setting From address for cronjob mails (because Gmail rejects)

Hello,

I have two identical CentOS 6.2 machines with
stock Postfix package and unchanged config:

# rpm -qa|grep post
postfix-2.6.6-2.2.el6_1.x86_64

# postconf -n
alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
debug_peer_level = 2
html_directory = no
inet_interfaces = localhost
inet_protocols = all
mail_owner = postfix
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
mydestination = $myhostname, localhost.$mydomain, localhost
newaliases_path = /usr/bin/newaliases.postfix
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.6.6/README_FILES
sample_directory = /usr/share/doc/postfix-2.6.6/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
unknown_local_recipient_reject_code = 550

On both machines I have appended

     afarber:     Alexander.Farber at gmail.com
     root:           Alexander.Farber at gmail.com

to the /etc/aliases and run "newaliases".

Both machines have several cronjobs and logwatch.

One machine is a database server,
I receive its cronjob mails just fine.

The other machine (preferans.de) is running Drupal 7.
I've configured it's MX records to point to Google Apps,
so that I can receive mails addressed to that domain
and this works well.

Also I've set Drupal's From address to
webmaster at prеferans.de  and so sending mails
by Drupal (for its user registration) works too.

But sending mails to my Gmail address by cronjobs
doesn't work. I suspect this happens, because
Google is too clever and it thinks
that mails coming from "preferans.de"
shouldn't have the From header set to
"afarber at static.169.40.9.176.clients.your-server.de"

Jan 20 09:34:10 static sendmail[10577]: q0K8Y7mj010577: from=afarber,
size=201, class=0, nrcpts=1,
msgid=<201201200834.q0K8Y7mj010577 at static.169.40.9.176.clients.your-server.de>,
relay=afarber at localhost
Jan 20 09:34:10 static postfix/smtpd[10578]: connect from
localhost.localdomain[127.0.0.1]
Jan 20 09:34:10 static postfix/smtpd[10578]: 9B84B31EA0A1:
client=localhost.localdomain[127.0.0.1]
Jan 20 09:34:10 static postfix/cleanup[10581]: 9B84B31EA0A1:
message-id=<201201200834.q0K8Y7mj010577 at static.169.40.9.176.clients.your-server.de>
Jan 20 09:34:10 static sendmail[10577]: q0K8Y7mj010577: to=afarber,
ctladdr=afarber (500/500), delay=00:00:03, xdelay=00:00:00,
mailer=relay, pri=30201, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0,
stat=Sent (Ok: queued as 9B84B31EA0A1)
Jan 20 09:34:10 static postfix/qmgr[10025]: 9B84B31EA0A1:
from=<afarber at static.169.40.9.176.clients.your-server.de>, size=823,
nrcpt=1 (queue active)
Jan 20 09:34:10 static postfix/smtp[10582]: connect to
static.169.40.9.176.clients.your-server.de[176.9.40.169]:25:
Connection refused
Jan 20 09:34:10 static postfix/smtp[10582]: 9B84B31EA0A1:
to=<afarber at static.169.40.9.176.clients.your-server.de>, relay=none,
delay=0.14, delays=0.12/0.01/0.01/0, dsn=4.4.1, status=deferred
(connect to static.169.40.9.176.clients.your-server.de[176.9.40.169]:25:
Connection refused)

So does anybody please have an
advice on how to fix my cronjob mails?

Regards
Alex