It looks like someone in northern Spain is sending out bulk e-mails and the Yahoo server is rejecting them. The mails are most likely originating from an innocent individual infected with a botnet mailer.
There is a little more to it than that... based on the mail header you posted... it appears that the mail server at bosauthsmtp01.eigbox.net is a misconfigured mail server. It looks like the assigned ip block where the mail server lives is 126.96.36.199/24 and is owned by 'Endurance International Group' according to the records[^]. The registered AS number for that IP block is AS29873[^] and you could attempt to contact them. In my experience... nobody every responds to abuse complaints unless there is a warrant attached.
The reason nobody responds to complaints probably has something to do with the fact that poor little Brian appears to be responsible for 79,461[^] domains within that ip range. And thats just one of the 51 ip blocks he appears to be responsible for.
Roger Wright wrote:Should I be concerned?
There isn't much you can do about it... the SMTP protocols were not very well designed and the protocol allows spoofing. It is up to the mail server software to prevent this. Your ISP or web hosting provider should be diligent with keeping the mail servers properly configured.
By the way you should probably remove your rawright.net[^] e-mail address from the mail header you posted. But because you left it there... I was able to determine that your domain name rawright.net at 188.8.131.52 is on the 184.108.40.206/18 ip block[^] which poor little Brian is responsible for[^]. I hope you don't mind... I hacked, probed and prodded your box a little bit... and it appears to be running IIS/6.0 on windows server.
I was able to connect to your rawright.net SMTP port 25 and forge my origin domain. The SMTP server did not complain. A well configured an e-mail server will perform a reverse DNS here and make sure my IP address matches the domain from the HELO command. I connected multiple times and each time I was routed through a different *.eigbox.net smtp authorization server. It looks like your service provider is using some sort of round robin BGP/GLBP routing.
I spent a few minutes manually testing your mail server via raw TCP socket but always recieved the error: 550 bosauthsmtp: Host x.x.x.x: No unauthenticated relaying permitted (I used all of the tricks I know about and was unable to trick the server into allowing me to relay mail. This is what we want). So maybe its already fixed. But maybe it is not fixed... if you look closely at the mail header you posted... it says the spam came via ESMTPSA which means the spam was sent over an encrypted TLS[^]. Although I would probably continue testing via TLSWrap[^]... I think I'll not test any further. It may be that their plain text SMTP server is well protected... but the encrypted SMTP is vulnerable.
Anyway we could speculate about this all day... but the best person to handle this would be a systems administrator from your rawright.net hosting provider.