This MR makes the example consistently use example-passwd. Currently example.com-passwd is used only in the line that this MR changes.
The line changed by this MR will fail because earlier in the example the file is named example-passwd rather than example.com-passwd.[1]
[1]:
To specify the authentication credentials, create an arbitrarily named file (e.g., '/etc/postfix/example-passwd'), with appropriately restrictive permissions (e.g., 600) containing a single line of the following form: