SPF softfail for forwarded emails to Gmail account
host.tariffplansindia.com is receiving a mail from outside, in this case
[email protected]. The receiver on your host is
[email protected]. Now your server relays that mail (without changing the envelope From-address) to gmail. The gmail server now gets a mail from your server
host.tariffplansindia.com with envelope-From
[email protected]. Now the SPF-Record of
hotmail.com forbids all senders except its own, and you can't do anything about that. SPF breaks this kind of mail-forwarding, that's a known issue, but it's also solved by Sender Rewriting Scheme (SRS) from Open SPF.
Using SRS, the relaying mailserver can rewrite the envelope-From so that it comes from a domain you control the SPF record for (
host.tariffplansindia.com). Unfortunately, setting up SRS on a mailserver requires - in most cases - compiling and installing software by hand, there is only a very limited variety of available implementations and also an existing question of how to perform SRS on postfix.