Link for signature in the mail

Hi,
I am testing the plugin i a multisite environment. But activated per subsite.
Everything is fine, but in the mail, there is the link to the signature related to the mainsite (gascht.com).
Like this:
/home/grischun/gascht.com/wp-content/uploads/….
I should have the link for this subsite example bergsunna.grischun.com like:
/home/grischun/bergsunna.gascht.com/wp-content/uploads/….
Where can I change this?
Thank you very much for help!
Regards
Martin