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"SMTP" and "SMTP Server" protocols--which to use?

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"SMTP" and "SMTP Server" protocols-... - 19.Jul.2004 11:08:00 PM

bluvg

Posts: 9
Joined: 6.Oct.2003
Status: offline

Just want to say--installed ISA 2004 last week--it's awesome! What a difference compared to the 2000 version!

Everything seems to be running fine except that occasionally some email is getting dropped, and I'm not really sure why (particularly why it's only happening from time to time). But here's something that I noticed in the logs that seemed to coincide with a dropped email report that I received from a colleague (who uses Message Labs, if it makes a difference): "SMTP Server" is allowed in, of course (via a mail server publishing rule), "SMTP" is allowed out as expected, but "SMTP" is not allowed in.

Checking the properties for the protocol, I see that "SMTP Server" is TCP port 25 inbound (from ISA's perspective) and "SMTP" is TCP port 25 outbound, so I can understand why it is blocked. But why are some external servers using "SMTP" (outbound from our perspective) to *send* mail? And is it safe to allow it in?

Thanks,
Ryan

Post #: 1

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RE: "SMTP" and "SMTP Server" protoc... - 20.Jul.2004 12:13:00 AM

tshinder

Posts: 47644
Joined: 10.Jan.2001
From: Texas
Status: offline

Hi Ryan,

"inbound" protocols are used only by Server Publishing Rules. Access Rules use "outbound" protocols. There should be no "outbound" SMTP rules that allow connections from External to Internal.

HTH<
Tom

(in reply to bluvg)

Post #: 2

RE: "SMTP" and "SMTP Server" protoc... - 20.Jul.2004 12:30:00 AM

bluvg

Posts: 9
Joined: 6.Oct.2003
Status: offline

Thanks, Tom--that is what I was thinking as well. However, I have a large number of entries in our logs of "SMTP" attempts from the External interface. One of these corresponds with the report I received of one of the messages that was dropped. Is there some reason their server would be sending email using this method? Could it be something to do with the redirect through Message Labs? I still need to figure out why some mail is getting dropped....

Thank you for your help!
Ryan

(in reply to bluvg)

Post #: 3

RE: "SMTP" and "SMTP Server" protoc... - 21.Jul.2004 1:24:00 AM

tshinder

Posts: 47644
Joined: 10.Jan.2001
From: Texas
Status: offline

Hi Ryan,

Not sure how MessageLabs is configured, but SMTP is the same whether its coming inbound or outbound. The difference with the "inbound" with ISA firewalls is that the destination is the IP address that you configured the connection to be accepted on at the ISA firewall.

HTH,
Tom

(in reply to bluvg)

Post #: 4