problem with sendmail, IP address lookup failed
 

I have sendmail and imap configured on a server in my closet, and i'm trying to set up thunderbird on my linux laptop and my windows xp desktop. i got imap working, and i've verified it works on all systems. when i try to send mail using smtp, i get this error:

An error occured while sending mail. The mail server responded: 5.7.1 <myemail@gmail.com>... Relaying denied. IP address lookup failed [192.168.1.1]. Please verify that your email address is correct in your Mail preferences and try again.


now, i got it on both my desktop and my laptop at first, but then i tweaked something on my laptop and suddenly it was working no problem. the last thing i remember doing was using copy & paste to copy the imap server name i had entered into the smtp server box (since imap was working). it started working, so i assumed i must've made a typo the first time. i've gone over all my settings on my desktop though, and i'm still getting the error.

all three computers are on a lan behind a linksys router. there are 5 computers total, and they're assigned IP addresses 192.168.100-105. the router is the dhcp host. the server is always 192.168.1.105, and i've logged in to the router and forwarded ports 22, 25, and 143 to that IP address. i have sendmail, sshd, imapd, and named running on the server. if necessary, i can give a full list of processes, but since i have it working on my laptop, my guess is the prolem lies in a configuration setting in thunderbird. any advice would be appreciated.

Have you added 192.168.1 to sendmail's access file to allow relaying?

i just read about that, so i set put this in /etc/mail/access:

192.168.1.1 OK
192.168.1 RELAY


i'm not sure what this does though...do i need to ajust my firewall? right now it lists 3 DNS servers:
2.4.4.5
2.4.4.6
2.4.4.7

if i tell the firewall to expect a DNS server at 192.168.1.105, and forward port 53 to that IP, then my desktop shows it as the first DNS server in it's list. but i tried that before and it didn't help, so i changed everything back.

ahaha! ok, i took out the first line i put in there about 192.168.1.1 and now it works. as a security question, what does this imply? what exactly is relaying? will i be able to use my smtp server from outside my LAN? and am i leaving myself open to spammers?

This configuration does not leave you open to spammers. You have relaying allowed only for 192.168.1.* and since that is an IP address that will never get publicly allocated then you are safe. Relaying means that the server accepts a mail message and passes it along to another mail server.

You won't be able to use the smtp server outside your lan exactly as you would from on the inside. It will be able to receive mail as usual but you won't be able to send mail through Thunderbird. If you forsee yourself needing to use it alot from outside your lan you could set up webmail. Squirrelmail is fairly easy to set up. http://www.squirrelmail.org/

or if i knew the IP address of my computer at work, say, i could add it to the relay list right?

Yes, that sounds good.

Also, while you are at it you could set your firewall to accept port 143 for only your work IP if it has that capability. That will at least keep people from trying to unneccessarily attack your IMAP server.