Add password_file to config.ini.

config/vufind/config.ini

@@ -700,6 +700,9 @@ host            = localhost
 port            = 25
 ;username       = user
 ;password       = pass
+; Use password_file to load the secret from another file instead of including it
+; directly in this configuration.
+;password_file = /path/to/secret
 ; If a login is required you can define which protocol to use for securing the
 ; connection. If no explicit protocol ('tls' or 'ssl') is configured, a protocol
 ; based on the configured port is chosen (587 -> tls, 487 -> ssl).