Emails redirected to @gmail.com getting marked as spam.

I am using aliases/redirects for some group emails. However users at gmail receive these group emails marked as SPAM in spam folder.

Some facts:

DKIM records are set correctly.
Mailserver is not in any blacklist db.
If I send regular email from/through poste.io mailserver directly to same [at]gmail recipients, then they receive emails just fine in inbox, so the problem is specifically if I send to aliases.
It was working fine for a while, but now for a approximately month it started being marked as spam, not sure if it was related to any poste.io updates or any updates at Gmail.

Here is the mail source from gmail, the one marked as spam: http://pastie.org/private/fclpo98ag5v0osu30ynf8a

I see following common pattern in headers of all messages being marked as spam:

Received-SPF: softfail (google.com: domain of transitioning [FROM_EMAIL_HERE] does not designate 144.76.18.119 as permitted sender) client-ip=144.76.18.119;
Authentication-Results: mx.google.com;
       spf=softfail (google.com: domain of transitioning [FROM_EMAIL_HERE] does not designate 144.76.18.119 as permitted sender) smtp.mailfrom=[FROM_EMAIL_HERE]
Received: (qmail 21698 invoked by uid 8); 15 May 2016 10:43:41 -0000

Is there anything I can do to avoid aliases to gmail being marked as spam? Thank you.

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