Sender address rejected: Domain not found - outgoing mail settings with Postfix

Environment:

A staging server called "tst.myserver.com", with no DNS record pointing to it.
Trying to send email from there to myself (me@my-mail.com)

Problem:

$ echo foo | mail -s bar me@my-mail.com
$ tail /var/log/mail.log
Jan 24 18:30:24 tst postfix/smtp[26306]: 46D8FC2584: to=<me@my-mail>, relay=mail.my-mail[1.2.3.4]:25, delay=0.61, delays=0.02/0.01/0.45/0.13, dsn=5.1.8, status=bounced (host my-mail[1.2.3.4] said: 554 5.1.8 <me@tst.myserver.com>: Sender address rejected: Domain not found (in reply to RCPT TO command))

Explanation:

$ cat /etc/hostname
tst.myserver.com
This is the FQDN (fully qualified domain name), and Postfix appends it to the local user name.

What we want

We'd like Postfix to append only the myserver.com and not the tst.myserver.com

A solution

(figured out by reading http://www.postfix.org/ADDRESS_REWRITING_README.html)
# vi /etc/postfix/main.cf
(add this line:)
masquerade_domains = myserver.com
Restart Postfix
# postfix stop && postfix start

Postfix error -- connect to transport private/smtp: Connection refused

Problem:

Cannot send out any email, except to local users

Environment:

UNIX (Linux, FreeBSD, etc)
Postfix

Symptoms:

/var/log/maillog has these messages:

warning: connect to transport private/smtp: Connection refused

Reason:

"unix" smtp is disabled in Postfix configuration

Fix:

Uncomment this line in master.cf

smtp unix - - n - - smtp

(there are two more lines about smtp - they deal with external connections. Need them only if you want to accept mail from outside, not to send mail)

Additional thing to check:

mailer.conf should look like this:

$ cat /etc/mail/mailer.conf

#

# Execute the Postfix sendmail program, named /usr/local/sbin/sendmail

#

sendmail        /usr/local/sbin/sendmail

send-mail       /usr/local/sbin/sendmail

mailq   /usr/local/sbin/sendmail

newaliases      /usr/local/sbin/sendmail