[Exim] fallback_hosts on smtp transport

Dear all,

Can I use different port for 'fallback_hosts' in my smtp transport, or does
the fallback_host always use the standard port 25?
What port does fallback_host use when I have a 'Port' option set on my smtp
transport?
After reading the doc, it is not quite clear to me...

what I would like to setup is:

tr_special:
  driver         = smtp
  gethostbyname
  hosts         = xyz.unifr.ch
  hosts_override
  fallback_hosts    = anotherhost.unifr.ch (on port 2525)

Thanks for any hint.
Regards
Hans-Peter