The mailing list for listmasters using Sympa

[eminmn <address@concealed>]

Thanks, Steve and Stephane. I have been study some of email headers 
lately and am confused by the great variety of tags (cc: user-agent: 
etc.) that seem to be present or absent without rhyme or reason. Do 
different mail clients show different information by default?

Ed


On 1/20/2017 02:12, Steve Shipway wrote:
> > > I thought that the list-owner(s)' email address was for members to get
> > > help from the list-owner(s). Has this line been added recently to
> > > address dmarc problems or has this line always been part of email
> > > headers? What does it mean or try to do?
> The Sender: header is very important for list servers, and has been defined 
> for decades.
>
> This header is mandated by the SMTP RFCs as the 'Secretary scenario'.  
> Basically, Sympa is like your secretary -- it sends out the emails on your 
> behalf.  So, while the email is *From* you, it was *Sent* by Sympa.
>
> This is an important distinction when you are looking at things like SIDF (otherwise 
> known as "evil bastard offspring of Microsoft and SPF") and DKIM, as well as 
> S/MIME signatures.  If the Sympa server is in a different domain or different server 
> from the original sender then it can trigger security warnings.
>
> The reason is that, if you are validating the source email address against 
> the SPF valid IP addresses for the domain, you need to compare against the 
> Sender (if it exists), not the From.  Otherwise, you'll see a message from 
> address@concealed actually coming from the mail servers of 
> address@concealed and flag it as a forgery.
>
> This is the root of the DMARC problems, because the DMARC RFC forgot about 
> this and mandated DKIM checks against the From header regardless, even if the 
> Sender header exists.  As a result, we have to break the SMTP RFC by changing 
> the From header (rather than just adding a Sender header) if we want to pass 
> DMARC checks.
>
> Steve
>
> ----
>
> Steve Shipway |  Senior Email Systems Administrator
> Phone: +64 9 302 0515 Fax: +64 9 302 0518
> Freephone: 0800 SMX SMX (769 769)
> SMX Limited: Level 15, 19 Victoria Street West, Auckland, New Zealand
> Web: http://smxemail.com
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