Line 70 from https://github.com/griffon/griffon-mail-plugin/blob/master/src/main/griffon/plugins/mail/MailSender.groovy shows that mailhost
is taken into account, at least when it comes to setting properties.
However this sounds more of a bug report than an actual question. If so I'd recommend you to post the issue to the Griffon user list. If it's found to be a bug then a report should be made to http://jira.codehaus.org/browse/griffon