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Problem with PIX 501 configuration for Exchange 5.5

I am trying to set up our PIX to allow mail in to and out of our Exchange server and can't figure out what is wrong with my configuration. Mail goes out no problem but I have only managed to get one message from my Hotmail account into the server, when I send other messages I receive NDR's. I need to get this up and running as soon as possible, any help would be much appreciated. I can't figure out what the problem is. Thanks in advance.

Current PIX configuration is as follows:

PIX Version 6.3(3)
interface ethernet0 auto
interface ethernet1 100full
nameif ethernet0 outside security0
nameif ethernet1 inside security100
enable password XXXXXXXXX encrypted
passwd XXXXXXXXX encrypted
hostname pixfirewall
fixup protocol dns maximum-length 512
fixup protocol ftp 21
fixup protocol h323 h225 1720
fixup protocol h323 ras 1718-1719
fixup protocol http 80
fixup protocol rsh 514
fixup protocol rtsp 554
fixup protocol sip 5060
fixup protocol sip udp 5060
fixup protocol skinny 2000
no fixup protocol smtp 25
fixup protocol sqlnet 1521
fixup protocol tftp 69
access-list smtp permit tcp any host eq smtp
pager lines 24
icmp deny any outside
icmp permit any inside
mtu outside 1500
mtu inside 1500
ip address outside
ip address inside
ip audit info action alarm
ip audit attack action alarm
pdm location inside
pdm location outside
pdm logging informational 100
pdm history enable
arp timeout 14400
global (outside) 10 interface
nat (inside) 10 0 0
static (inside,outside) netmask 0 0
access-group smtp in interface outside
route outside 1
timeout xlate 0:05:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00
timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00
timeout uauth 0:05:00 absolute
aaa-server TACACS+ protocol tacacs+
aaa-server RADIUS protocol radius
aaa-server LOCAL protocol local
http server enable
http inside
no snmp-server location
no snmp-server contact
snmp-server community public
no snmp-server enable traps
floodguard enable
telnet inside
telnet inside
telnet timeout 5
ssh timeout 5
console timeout 0
dhcpd address inside
dhcpd dns
dhcpd wins
dhcpd lease 518400
dhcpd ping_timeout 750
dhcpd domain XXXXXXXX
dhcpd auto_config outside
terminal width 80
: end

Avatar of srgilani
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telnet your server from outside on port 25 and paste output.
if you are able to telnet then better way to diagnose is check outside mail server logs and see what problem its facing while talking to exchange inside pix.

If you change your config to include the below. Replace A.B.C.D with the IP address of your mail server/filter.

fixup protocol smtp 25
static (inside,outside) tcp interface 25 A.B.C.D 25 netmask 0 0
no access-list 101
access-list 101 permit tcp any any eq 25
Avatar of Les Moore
Karma AU - You can't enable fixup smtp with Exchange 5.5

Your access-list is fine and your existing static is fine. What kind of WAN link do you have? DSL? Cable? Other? Are you sure the ISP is routing the complete .248 subnet to you? Are you sure you have published the correct IP in the MX records for DNS? Who is your primary DNS for your domain? Your ISP?
Avatar of stephmanz


Thanks for the responses.
When I telnet on port 25 from outside the connection fails to open.

It's a 2mb DSL line.
The subnet I have been given is
MX lookup gives the .27 address. Primary DNS is our ISP, called Lumison.
According to the A record in DNS for the domain is Hope this is of some help.
Use this tool to test your domain name:

Can you verify the default gateway and the subnet mask settings on the Exchange server? It needs to point to the PIX as the default gateway.

Can you use "sho access-list" and see if you are getting any hitcounts on the access-list entry? If yes, then we look primarily at the server. If no, then we look at other things.

Your Exchange server is .104 and this appears to be in the middle of your DHCP scope, and it needs to be a static IP address on the server.
 >dhcpd address inside

You can end up with an ip address conflict this way. Change the server's internal IP to something outside this scope (like .144), or change the scope to exclude .104

One other alternative is to change the dns max-length:
  no fixup protocol dns maximum-length 512
  fixup protocol dns maximum-length 1024

Output from sho access-list is

access-list cached ACL log flows: total 0, denied 0 (deny-flow-max 256)
            alert-interval 300
access-list smtp; 1 elements
access-list smtp line 1 permit tcp any host eq smtp (hitcnt=4)

Exchange server ip is static as follows

The DHCP functionality on the PIX is disabled, those entries are a throwback to an earlier configuration.
> (hitcnt=4)
This indicates that the configuration is allowing at least some packets in.

The server IP config looks good. How about the DNS server .4 ?

Did you try changing the DNS max-length in the fixup?
Thanks, will try the max-length over the weekend.
Hi, have change the max length and no change unfortunately. Mail goes out fine but nothing's coming in.
Did you get any clues from dnsreports ?
There are a few failures:

Missing (stealth) nameservers
Stealth NS record leakage
Duplicate MX records (the ISP's mail servers not ours)
No reverse DNS entry for our MX record, I asked our ISP's tech support about this and they assured me it wasn't necessary.
Couldn't connect to our mail server .
A warning about glue at parent nameservers.

I feel uneasy about the reverse DNS situation but will happily accept that I am mistaken. The mailserver in our other office has a reverse lookup so I've asked our ISP to create one for this MX.
You should feel uneasy about the reverse dns. It is necessary.
Duplicate MX records could be a big problem and the reason you aren't getting any email.
It appears to be a DNS issue.
I believe you are correct. No response from my ISP as yet and their phones are constantly busy. Do you mind if I keep this question open a while longer until I've heard back from them ?
Avatar of Les Moore
Les Moore
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Thanks. Well, I installed our spare PIX 506E from our other office. I redid the configuration from scratch, logged onto my Hotmail account and sent a message which arrived. Tried again and this one failed, I don't understand how it can work once and then fall over like this.
reverse dns should be present. or if your mail depends on ISP mail servers ask them to resolve duplicate MX problem.
It turns out my ISP had a misconfigured rule on one of their firewalls and inbound mail was being blocked. Has been working as it should for a few days now. Thank you very much for your help.
Dammit - darned ISP's. . . . takes forever to find someone with IQ over 65 to help out . . .

Thanks for the update!
- Cheers!