Monthly Archives: September 2016

Message Delivery Testing with Exim

Email DeliveryI was recently doing some troubleshooting of email delivery on an Exim server.

I wanted to see what happens when the server attempts delivery. The error in the logs was a timeout, but it does not tell you when in the process the timeout happens.

Brad the Mad has a nice Exim Cheatsheet online that gives some examples of how to manage an Exim server.

Expanding on some of his examples I used this command:

exim -v -M <message-id>

That command will force Exim to attempt a delivery of the message you define as the message-id. The addition of -v will show every step of the process, very handy.

In my test using this tool, the delivery failed. In fact, it could not even connect to the remote server at all. Yet, if I did a telnet command like this:

telnet 123.345.679.123 25

I could connect to the remote server. After some digging, I found the exim.conf file was using a command on the transport to bind the outbound connections to an IP address on the server other than the default IP.

interface      = <; 192.168.123.123

The network then had special rules on the firewall to direct outbound traffic from that IP address to a specific public IP address.

So my telnet command that was giving me a positive result, I could connect to the remove server but only because my test was not simulating the same outbound IP address as the server.

If you need to telnet out of a server and bind to a specific IP address, you can do it like this:

telnet -b <sourceaddress> <destination> <port>

Bonded Internet

A quick post for people who rely on ADSL connections for their Internet.

If you need more power take a look at iTel, they offer a bonded Internet connection where you can bond up-to 6 connections for ‘mega bandwidth’.

300 FiberI’m happy to say I currently enjoy a 300 meg fiber connection (yes, I’m bragging) so I don’t have a need for bonded ADSL now but perhaps in the future.

How bonded ADSL work?

Bonded ADSL is where multiple ADSL lines are combined into a single aggregated connection to deliver greater download and upload speeds. This is not the same as using a load balancing router with multiple connections.

With bonding, the original datastream is split up into multiple streams, each of which is sent down an individual ADSL connection. The process of splitting datastreams is performed by special hardware at the bonded ADSL provider’s datacentre. At the customer’s premises, the separate datastreams are recombined to form a single data stream.

A super cool way to increase your bandwidth when only ADSL is available.