My first guess was that your remote mailserver (ISP's) was down. I did a quick check and it appears up:
[root@inet01 /root]# telnet mail.iinet.net.au 25
Trying 203.0.178.192...
Connected to mail.iinet.net.au.
Escape character is '^]'.
220 mail-06.iinet.net.au ESMTP
EHLO
250-mail-06.iinet.net.au
250 8BITMIME
HELO
250 mail-06.iinet.net.au
BYE
502 unimplemented (#5.5.1)
QUIT
221 mail-06.iinet.net.au
Connection closed by foreign host.
If you have SSH/Telnet access enabled on your server you can login using the admin account and you should be able to configure the SME server from the administrative console using Lynx. On 4.X I think it's like option 5 or 6. If you can't get in using your admin login, use root and invoke /sbin/e-smith/console
Hope this helped,
Nathan