Need Allowing SMTP traffic from my network only BLOCK outside network to used SMTP.

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Apr 9th, 2010
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Dear Experts,

I have facing very much problem of SMTP traffic , lots of unknown outside the network used my mail server SMTP port,

heavy much mail send through my mail server ( used SMTP port) from outside network.

I need it to block smtp port from outside network , only allowed from my network.

i am using Cisco 3845 router.

my Mail server IP

If I put in access lists for each range and nothing else associated with SMTP would that accomplish the task?

Allowing SMTP traffic from on a few IP ranges ( my network only BLOCK outside network need to configure my Cisco 3845 to only allow SMTP traffic from certain IP ranges to my mail server

so what i can do to solve this issue.

my network



So plese give me the soluction regarding the same.

Any help would be great!



Allowing SMTP traffic from on a few IP ranges

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Jennifer Halim Sat, 04/10/2010 - 00:06
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You would need to configure your mail server to not allow mail relay through it.

Don't think you can block mail traffic from outside with an access-list, as it will block legitimate mail traffic inbound.

csawest.dc Sat, 04/10/2010 - 00:11
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Dear Halijenn,

I already congured in my mail server ( no mail relay). but still facing the problem i need to block smtp through outside the network.

Thanks in ADV,


Jennifer Halim Sat, 04/10/2010 - 00:16
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You would need to have Mail gateway, like Iron Port or CSC module on ASA firewall for example to be able to block those traffic. With access-list, you would be blocking legitimate mail traffic as well because access-list only looks at layer 3/4, not deep into the email itself.

csawest.dc Sat, 04/10/2010 - 00:24
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Dear Friend,

I need to config in my router SMTP port not allowed to used of outside the network , it;s only allowed my network ips only. other ips block to used SMTP



paolo bevilacqua Sat, 04/10/2010 - 03:11
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Do you understand how email in the internet works ?

Are you able to configure correctly an email server ?

From your posts above, seems like the answer to both questions is "no".

In that case, I recommend you engage a reputable IT professional to help you.


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