This is spoofed.
Received: from mail.vistomail.com (cpe-104-231-205-87.wi.res.rr.com
[104.231.205.87])
by smtp1.linuxfoundation.org (Postfix) with SMTP id 01BCADF
for ;
Thu, 10 Dec 2015 06:53:42 +0000 (UTC)
104.231.205.87 is not mail.vistomail.com. It's some residential IP, cpe-104-231-205-87.wi.res.rr.com.
I feel like the mailing list must be seriously misconfigured to allow this sort of spoofing... You could exploit this to send mail "from" any of the devs, for example.
Yup Vistomail, should be coming from the below subnet or possibly the below IPs.
> set type=mx
> vistomail.com
Non-authoritative answer:
vistomail.com MX preference = 10, mail exchanger = vistomail.com
vistomail.com internet address = 190.97.163.93
> mail.vistomail.com
Non-authoritative answer:
Name: vistomail.com
Address: 190.97.163.93
Aliases: mail.vistomail.com
>