If my situation is

I have two mail servers mys1 and mys2, and each of these use an outside mailserver "others1" as a smarthost.

Recently , due to some security modifications, the "others1" is accepting messages from mys2 but not delivering them. (mail from mys1 is unaffected)

Could I workaround this by getting mys2 to use mys1 as a smarthost? (thus having "nested" smarthosts).

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On 8/4/21 7:09 PM, Nick Hocking wrote:

Could I workaround this by getting mys2 to use mys1 as a
smarthost? (thus having "nested" smarthosts).

Probably.

But I'd suggest investigating why others1 is not delivering messages
like it has been ~> probably should be.



--
Grant. . . .
unix || die

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On Friday, August 6, 2021 at 1:40:56 PM UTC+10, Grant Taylor wrote:

On 8/4/21 7:09 PM, Nick Hocking wrote:

Could I workaround this by getting mys2 to use mys1 as a
smarthost? (thus having "nested" smarthosts).

Probably.

But I'd suggest investigating why others1 is not delivering messages
like it has been ~> probably should be.

--
Grant. . . .
unix || die

Hi Grant,
Yep - Nested smarthosts worked like a charm. Not sure I can think of a really good use for this.

Maybe a large University with many campus each with many departments, thus allowing central distribution list administration and only one external facing mailer having to worry about spam and malware etc.

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On 8/8/21 1:11 AM, Nick Hocking wrote:

Hi Grant,

Hi Nick,

Yep - Nested smarthosts worked like a charm. Not sure I can think of
a really good use for this.

:-)

Maybe a large University with many campus each with many departments,
thus allowing central distribution list administration and only one
external facing mailer having to worry about spam and malware etc.

I tend to think of this as a complex SMTP network. As in it's more than
just one server to the Internet and done.

The few times that I've been exposed to such complex SMTP networks have
largely been fairly short (fewer layers) and wide (many servers). As in
most ~> all application / file / database / etc. servers were configured
to use the / a "smart host". The smart host(s) were configured with
knowledge of where to send messages based on recipient(s); e.g. inter-department email. The smart host(s) may send directly to the
Internet, or they may send through another (set of) smart host(s) that
serve as the outbound queue for message leaving the network. The
outbound servers dealt with the retries and transient failures of
outbound email thereby allowing the queue(s) on the smart host(s) to be
fairly clean and not back up there for more than a few minutes. Usually inbound email passed through email hygiene appliance(s) / server(s).
Sometimes outbound messages did as well. So, you ended up with the leaf servers, the central smart host(s), and an outbound leaf (set). In some
ways reminiscent of a three tiered Clos network from an SMTP perspective.



--
Grant. . . .
unix || die

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On Monday, August 9, 2021 at 6:40:01 AM UTC+10, Grant Taylor wrote:

On 8/8/21 1:11 AM, Nick Hocking wrote:

Hi Grant,

Hi Nick,

Yep - Nested smarthosts worked like a charm. Not sure I can think of
a really good use for this.

:-)

Maybe a large University with many campus each with many departments,
thus allowing central distribution list administration and only one external facing mailer having to worry about spam and malware etc.

I tend to think of this as a complex SMTP network. As in it's more than
just one server to the Internet and done.

The few times that I've been exposed to such complex SMTP networks have largely been fairly short (fewer layers) and wide (many servers). As in
most ~> all application / file / database / etc. servers were configured
to use the / a "smart host". The smart host(s) were configured with
knowledge of where to send messages based on recipient(s); e.g. inter-department email. The smart host(s) may send directly to the
Internet, or they may send through another (set of) smart host(s) that
serve as the outbound queue for message leaving the network. The
outbound servers dealt with the retries and transient failures of
outbound email thereby allowing the queue(s) on the smart host(s) to be fairly clean and not back up there for more than a few minutes. Usually inbound email passed through email hygiene appliance(s) / server(s). Sometimes outbound messages did as well. So, you ended up with the leaf servers, the central smart host(s), and an outbound leaf (set). In some
ways reminiscent of a three tiered Clos network from an SMTP perspective.
--
Grant. . . .
unix || die

Hi Grant,
In these complex SMPT networks, did they have the corresponding network routing/firewall stuff done on the servers (using firewalld, for example) or did they have dedicated network routers/firewalls?

Nick

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On 8/8/21 11:56 PM, Nick Hocking wrote:

Hi Grant,

Hi,

In these complex SMPT networks, did they have the corresponding
network routing/firewall stuff done on the servers (using firewalld,
for example) or did they have dedicated network routers/firewalls?

They had accompanying network routers / firewalls, all dedicated
hardware. (Firewalld wasn't a thing, much less an allowed option.)
These were a mixture of platforms; Intel x86, Sun SPARC, IBM RS/6000,
IBM AS/400, IBM Mainframe, along with their associated OSs; Microsoft
Windows, Novell NetWare, IBM OS/2, IBM AIX, IBM OS/400, IBM z/OS, Sun
Solaris, SCO OpenServer / UnixWare, FreeBSD, Red Hat Linux, (Open)SuSE
Linux, Gentoo Linux, what have you. It was multiple thousand systems in
a complex enterprise network. I was speaking about the SMTP network
created by the systems using independent software speaking the common
(E)SMTP protocol.



--
Grant. . . .
unix || die

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