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Block SMTP on ASA 5500

Posted on 2011-02-15
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Last Modified: 2012-05-11
Hello we would like it so that only the exchange server is allowed to send email out from the network. We have had some issues where users have taken their virus infected home computer to the office. How can we setup the ASA so that it only allows the exchange server to send email on port 25?

This is my acl:

access-list outside_access_in extended permit tcp any host 213.145.177.74 eq smtp
access-list outside_access_in extended permit tcp any host 213.145.177.74 eq https
access-list outside_access_in extended permit tcp host 10.10.1.1 any eq smtp
access-list outside_access_in extended permit tcp host 10.10.1.202 any eq smtp
access-list outside_access_in extended deny tcp any any eq smtp

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Question by:daxa78
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6 Comments
 
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Ernie Beek earned 500 total points
ID: 34896355
You have to create an accesslist on the inside interface, something like:

access-list inside_access_out extended permit tcp host x.x.x.x any eq smtp (x.x.x.x = exchange server)
access-list inside_access_out extended deny tcp any any eq smtp
access-list inside_access_out extended permit ip any any


That should do the trick.
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Author Comment

by:daxa78
ID: 34896498
So i should just delete those other acl?

Thx
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LVL 35

Expert Comment

by:Ernie Beek
ID: 34896525
Well, no. Those are the incoming rules. I think you still want your exchange server to be reachable don't you? You might to have a look to see if anything can be removed (i see three times incoming smtp).
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Author Comment

by:daxa78
ID: 34896685
Did not work this is what my acl looks like now.

All host on the network can still connect to smtp servers on the outside.

access-list inside_access_out extended permit tcp host 10.10.1.1 any eq smtp
access-list inside_access_out extended permit tcp host 10.10.1.202 any eq smtp
access-list inside_access_out extended deny tcp any any eq smtp
access-list inside_access_out extended permit ip any any
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LVL 35

Assisted Solution

by:Ernie Beek
Ernie Beek earned 500 total points
ID: 34896774
Eh, did you also issue: acces-group inside_access_out in interface inside ?

Assuming the name of your inside interface is 'inside'.
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LVL 35

Expert Comment

by:Ernie Beek
ID: 34897608
Thanks for the points.

Regarding your outside accesslist, you might want to remove:


access-list outside_access_in extended permit tcp host 10.10.1.1 any eq smtp
access-list outside_access_in extended permit tcp host 10.10.1.202 any eq smtp
access-list outside_access_in extended deny tcp any any eq smtp


There's no need for those and there's allways an implicit 'deny all' at the end of an access list.
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