<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML ><HEAD ><TITLE >( SMTP Relay ) - Internal MASQed computers cannot send SMTP or POP-3 mail!</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="Linux IP Masquerade HOWTO" HREF="index.html"><LINK REL="UP" TITLE="Frequently Asked Questions" HREF="faq.html"><LINK REL="PREVIOUS" TITLE="( Stops working ) - IP MASQ works fine for a while but then it stops working. A reboot seems to fix this. Why?" HREF="masq-stops-working.html"><LINK REL="NEXT" TITLE="( Source Routing ) - I need different internal MASQed networks to exit on different external IP addresses" HREF="iproute2.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Linux IP Masquerade HOWTO</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="masq-stops-working.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 7. Frequently Asked Questions</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="iproute2.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="SMTP" ></A >7.38. ( SMTP Relay ) - Internal MASQed computers cannot send SMTP or POP-3 mail!</H1 ><P > Though this isn't a Masquerading issue but many users do this so it should be mentioned. </P ><P >SMTP: The issue is that you are probably using your Linux box as an SMTP relay server and get the following error:</P ><P > <TABLE BORDER="1" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><FONT COLOR="#000000" ><PRE CLASS="SCREEN" >"error from mail server: we do not relay"</PRE ></FONT ></TD ></TR ></TABLE > Newer versions of Sendmail and other Mail Transfer Agents (MTAs) disable relaying by default (this is a good thing). So do the following to fix this:</P ><P > <P ></P ><UL ><LI ><P >Sendmail: Enable specific relaying for your internal MASQed machines by editing the /etc/sendmail.cw file and add the hostname and domain name of your internal MASQed machine. You should also check to see that the /etc/hosts file has the IP address and Fully Qualified Domain Name (FQDN) configured in it. Once this is done, you need to restart Sendmail for it to re-read its configuration files. This is covered in <A HREF="http://www.ecst.csuchico.edu/~dranch/LINUX/index-linux.html#TrinityOS" TARGET="_top" >TrinityOS - Section 25</A > </P ></LI ></UL > </P ><P >POP-3: Some users configure their internal MASQ'ed computer's POP-3 clients to connect to some external SMTP server. While this is fine, many SMTP servers out there will try to IDENT your connection on port 113. Most likely your problem stems around your default Masquerade policy being set to DENY. This is BAD. Set it to REJECT and re-run your rc.firewall-* ruleset.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="masq-stops-working.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="iproute2.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >( Stops working ) - IP MASQ works fine for a while but then it stops working. A reboot seems to fix this. Why?</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="faq.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >( Source Routing ) - I need different internal MASQed networks to exit on different external IP addresses</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
