Forward root email to other email via postfix relay, strange problem

[plaguebreath]

First of all sorry for my english and thank you for help me in my difficult journey to learn Linux and by this using CentOs on an old HP ML110 I had chance to put hands on. Basically I fresh installed Centos 7 on a software raid 1 and that's the happy part of it. After that my next step was to get email from mdadm after some incident happen to my raid for doing that I set up Postfix (sendonly) only for relay my emails to my web provider SMTP server. And that's worked too after I testing with the:
echo "This is the body of the email" | mail -s "This is the subject line" gggg@xxxx.com
I got email correctly but from my user called root@domain.local
Now I would like to try to forward email sent from mdadm to root (or any mail sent from services to it) to my external address gggg@xxxx.com from an email like noreply@xxxx.com so first I try with for ~/forward and with Alias but at the end for change the FROM part I follow the suggestion here
https://serverfault.com/a/674984
but now the strage part of it is that if I test with mdadm email I get as result an email with FROM and TO uqual to noreply@xxxx.com but email is correctly delivered to my email address gggg@xxxx.com so what can I do for try to fix it ?
Every mail sent only to root has same TO address. Thank you for the help I really enjoy learning.

[poky]

Try insert line to /root/.mailrc:
set from=noreply@xxxx.com

[plaguebreath]

I try your solution, then I did a test on mdadm
mdadm --monitor --scan --test --oneshot /dev/md[[:digit:]]*
the results is email like :

FROM: centos1@mydomain.it
TO: root@centos1.localdomain

while my address is myaddress@mydomain.it

my /root/.forward is set with myaddress@mydomain.it
for setting the sender from my centos server I use this setting on postfix
change in /etc/postfix/main.cf

Code: Select all

sender_canonical_classes = envelope_sender, header_sender
sender_canonical_maps =  regexp:/etc/postfix/sender_canonical_maps
smtp_header_checks = regexp:/etc/postfix/header_check

I edit the file /etc/postfix/sender_canonical_maps

Code: Select all

/.+/    centos1@mydomain.it

I edit the file /etc/postfix/header_check

Code: Select all

/From:.*/ REPLACE From: centos1@mydomain.it

Still not working

[plaguebreath]

Ok seems I got it working, tell me if I did wrong please
I add to /etc/postfix/header_check

Code: Select all

/^To: root*/ REPLACE to: myaddress@mydomain.it

and now the header of the email that being forwarded from user root being correcty edited on header with the forward address.
Not very stylish but at least working
What you think about it ?