Hi, Mike -
On 16 August 2016 at 13:46, Mike Tubby <mike@???> wrote:
> When a sending MTA or MUA looks up the MX for the domain it gets two equal
> choices (relay1 and relay2) and randomly picks one - half the traffic comes
> in on each of relay1 and relay2.
Hmm… You must be using unusual MUA software. Most user email clients need
to be explicitly configured with an "Outgoing SMTP server" and don't look
up MX records; instead such records are for MTAs such as Exim.
Hence we use MX records as you describe to have MTAs here and elsewhere
route incoming email to our relays, but the load-balanced SMTP/AuthSMTP IP
address for email clients, printers, scanning electron microscopes, etc to
submit their generated emails to.
We actually block outbound connections to port 25 on external servers so
that all outbound mail has to be relayed through our gateways for logging
purposes. So even if an MUA here did happen to do MX lookups and use those
it wouldn't be able to connect/transmit its outgoing message.
Cheers,
Mike B-)
--
Systems Administrator & Change Manager
IT Services, University of York, Heslington, York YO10 5DD, UK
Tel: +44-(0)1904-323811
Web:
www.york.ac.uk/it-services
Disclaimer:
www.york.ac.uk/docs/disclaimer/email.htm
