Better Use <int:header-enricher/> instead of <int-mail:header-enricher/>

<int:header-enricher id="mailHeaderEnricher" input-channel="channel-in" output-channel="outboundMail">
<int:header name="mail_subject" expression="'Ex : ' + payload" />
<int:header name="mail_to" value="XXX@gmail.com" />
<int:header name="mail_from" value="XXX@gmail.com" />
</int:header-enricher>