Some ISP's are now blocking outgoing port 25 which prevents user from using smtp via their server. The workaround is to get exim to listen on another port other than 25 to bypass the ISP's block.
For example, to get exim to listen on both port 25 and port 587, you'd add the following code to the very top of the /etc/exim.conf file:
daemon_smtp_ports = 25 : 587
Once saved, restart exim:
Redhat:
/sbin/service exim restart
FreeBSD:
/usr/local/etc/rc.d/exim restart
More info:
The default case in an IPv6 environment is
daemon_smtp_port = smtp\\ local_interfaces = <; ::0 ; 0.0.0.0\\
This specifies listening on the smtp port on all IPv6 and IPv4 interfaces. Either one or two sockets may be used, depending on the characteristics of the TCP/IP stack. (This is complicated and messy; for more information, read the comments in the daemon.c source file.)
To specify listening on ports 25 and 26 on all interfaces:
daemon_smtp_ports = 25 : 26\\
(leaving local_interfaces at the default setting) or, more explicitly:
local_interfaces = <; ::0.25 ; ::0.26 \
0.0.0.0.25 ; 0.0.0.0.26
To listen on the default port on all IPv4 interfaces, and on port 26 on the IPv4 loopback address only:
local_interfaces = 0.0.0.0 : 127.0.0.1.26
To specify listening on the default port on specific interfaces only:
local_interfaces = 192.168.34.67 : 192.168.34.67
Note: such a setting excludes listening on the loopback interfaces.