On Thursday, December 2, 2004, 16:29:10, T. Bradley Dean wrote:
> ...
> IN MX 10 mx
> mx IN A 1.2.3.2
> mail IN A 1.2.3.4
>
> All domains will use the same mx with the same IP (1.2.3.2), but, like you
> said before, the Baracuda will then forward to different IPs for
> mail.Domain1.com, mail.Domain2.com, mail.Domain3.com, etc.
> ...
> Assuming all the above is correct, what's to keep spammers from
> mailing to my old mx of mail.Domain.com (1.2.3.4)? It would bypass the
> mx firewall and go into iMail directly.
What keeps them out is your firewall configured to block incoming SMTP
access to anything other than 1.2.3.2.
> How common is this? If they port scan they are going to get a hit,
Theres no doubt about it if you leave it open.
> I have to keep outside SMTP access to iMail for my users.
There are other alternatives:
- make them relay thru their ISP when they're 'outside'
- have them establish a VPN connection
- configure your firewall to port forward some other (e.g. 2525) port to
your internal port 25
- see if the Barracuda can transparently proxy SMTP AUTH requests to
your IMail box
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