[exim] Alias to external server and SPF failure

Hello!

FreeBSD, Exim 4.71 + MySQL

I have Alias router defined as:
mysql_alias:
      driver = redirect
      domains = +local_domains
      allow_fail
      allow_defer
      data = ${lookup mysql {SELECT send_to FROM mail_alias WHERE
      mail_domain='${quote_mysql:$domain}'
      AND mail_user='${quote_mysql:$local_part}'}}

All work ok until "send_to" columns = login@??? or
external domain without SPF checking.

Problems starts when target server have strong SPF checking.
For example when user sent mail
from: login@??? (wp.pl is one of biggest web portals in Poland)
to alias: login@???
target mail: other@???

I suppose I must rewrite "FROM" mail to login@???
AND put login@??? to "REPLY-TO" and then SPF checking will pass.

How can I do that best?

Best Regards!