Troubleshooting a Postfix Installation

First, we verify the reported issue by conducting our own test.

telnet localhost smtp
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 server1.example.com ESMTP Postfix

ehlo localhost
250-server1.example.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN

mail from: [email protected]
250 2.1.0 Ok

rcpt to: [email protected]
454 4.7.1 <[email protected]>: Relay access denied

quit
221 2.0.0 Bye

Relay access denied means there's something wrong with the postfix configuration. If we look at /etc/postfix/main.cf, we find that the mydestination setting has this:

mydestination = $myhostname, localhost.$mydomain, localhost

It's missing the $mydomain setting at the end of the line. So changing it to:

mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain

Then restart postfix to resolve the error.

telnet localhost smtp

Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 server1.example.com ESMTP Postfix

ehlo localhost
250-server1.example.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN

mail from: [email protected]
250 2.1.0 Ok

rcpt to: [email protected]
250 2.1.5 Ok

data
354 End data with <CR><LF>.<CR><LF>

test.
.
250 2.0.0 Ok: queued as 9B26C97CBF

quit
221 2.0.0 Bye
Connection closed by foreign host.

The easiest way in my experience is to first verify the alias_maps setting in postfix's main.cf.

grep alias_maps /etc/postfix/main.cf
...
alias_maps = hash:/etc/aliases
...

After making sure that's set to hash:/etc/aliases, we can edit /etc/aliases and make sure there's a root: cloud_user line at the end, and then run the newaliases command.