[lxc-users] sendmail / use IP of host ? / network.type=none

[Dr. Helmut Emmelmann]

Marat Khalili <mkh at rqc.ru>:

>> I am afraid, that spam filters receiving emails from it
>> will rate emails down, because of the NAT and the private IP.
> It's NAT that already gives your container access to public IP and also
> protects it from spammers outside. There are other ways but you really
> don't need them unless you want to receive mail too.

The server receives email and that works well in my experiments (using  
DNAT rules).
In fact the server is intended as mail hosting server, that has sendmail and
cyrus to host mail boxes for our clients and acts as mail relay / smart host
for authorised clients.

>
> If you care about your reputation against spam filters, make sure your
> public IP has DNS record (most likely your ISP already took care of
> this),

The public IP is in the DNS, however sendmail believes to work on the virtual
host in the container with a private IP and a private host name.
So it logs this private host name in the received mail headers,
uses it in the EHLO message, etc, which is against RFC 2821. Therefore the
outgoing and authorised-relayed mails show the private host name
in the received headers while they should have the public host name
that is in the DNS.

It is possible to set the host name used by sendmail
(using sendmail confDOMAIN_NAME)
which some people do to overcome the problems with NAT.
This also works fine in my simple tests, but obviously I
cannot test every possible situation.
The sendmail docs recommend to use this option only for sitations in that
local domain name cannot be determined.

So if there are other ways to give sendmail access to the real
ip on the host, I'd like to check them out.

Thank you very much,
Helmut Emmelmann



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