Re: Mail Transport ports

[Greg Baumgratz]

Yes, tcp connections.  What exactly I am attempting to do is limit incoming connections to only those for smtp and pop3 connections, which I have effectively done bycreating an access list that allows incoming tcp connections on port 25 (smtp) from any ip address, allows incoming tcp connections on port 110 (pop3) from and ip address, and denies any other packets incoming(tcp).  Lets forget about the DNS issue for now.  This solves the problem and mail is delivered to my server without incident.  The problem arises when the server attempts to send mail to another server as it does so on smtp port 25.  The return packets come on a higher connection and are thus denied.  Just wanted to explain the situation a little better in case I confused some. As for you statement about blocking the source ports, I agree with you on this subject, but what I actually wanted to do was 'permit' by source port.  In other words, all responses to my smtp connection that come back have the allocated port for the destination port, but always (i think) have a source port of 25. Thanks, Greg Klint Gore wrote: They're not udp. ims opens a tcp connection to remote port 25 using whatever local port windows gave it. all communication happens on that single connection. windows tends to allocate the next free port >1024. In firewalls, it's traditional to block the destinations (for incoming connections on the local interface, for outgoing connections on the wan interface). not many people block source ports as they are usually allocated by the ip stack not set by the application. klint. On Tue, 13 Jan 2004 16:20:22 -0500, Ted <[EMAIL PROTECTED]> wrote: I can't help with the IMS ports, but depending on what cisco firewall/router you're running, most of them can permit/deny on source port as well as destination port. It is just not used that often. BTW, are all the response messages you mentioned below UDP? Greg Baumgratz wrote: Here's a question: When your mail server sends mail by smtp it goes out on port 25. Any ideas of the range the responses will come on? When your server receives mail, the connection will always be incoming on port 25, but when you send messages from your server, they will go out 25 and the responses messages will come on other ports. The reason behind this is if in your router, you block all packets to your mailserver other than port 25, you can receive mail without a problem, but you can no longer send mail. I have recorded packets in the 2000s and 3000s as reponse messages, of course coming with a source port of 25. As far as I know, you can not permit packets in the cisco based on source port, only destination. Is there a rule that defines the ports the responses will return on? Greg This is the discussion list for the IMS Free email server software. To unsubscribe send mailto:[EMAIL PROTECTED] Delivered by Rockliffe MailSite http://www.rockliffe.com/mailsite Rock Solid Software (tm) This is the discussion list for the IMS Free email server software. To unsubscribe send mailto:[EMAIL PROTECTED] Delivered by Rockliffe MailSite http://www.rockliffe.com/mailsite Rock Solid Software (tm) +---------------------------------------+-----------------+ : Klint Gore : "Non rhyming : : EMail : [EMAIL PROTECTED] : slang - the : : Snail : A.B.R.I. : possibilities : : Mail University of New England : are useless" : : Armidale NSW 2351 Australia : L.J.J. : : Fax : +61 2 6772 5376 : : +---------------------------------------+-----------------+ This is the discussion list for the IMS Free email server software. To unsubscribe send mailto:[EMAIL PROTECTED] Delivered by Rockliffe MailSite http://www.rockliffe.com/mailsite Rock Solid Software (tm)