Action Mailer and ApplicationHelper method

Hi,

sorry if this has been asked before, but I couldn’t find any info. Is
it possible to use application helper methods in ActionMailer
templates (or methods, in case this is the only way)? All I found is
one statement in the agile web development book, that ‘the regular
helper methods, such as truncate(), are available’.
Is there any overview which helpers are available, as I know that
e.g. link_to doesn’t work.
BTW, Is there any possibility to get at least the base server address
in an action mailer, to send a link in the email?

Thanks for any help
Rainer Frey