Problem: Switching from IPCop to Endian Community 3 resulted in Outlook not connecting to the Office 365 servers.

Solution: It appears the issue is with Squid (see http://www.squid-cache.org/mail-archive/squid-users/201308/0269.html). Office 365 resolves outlook.office365.com to 25 different addresses, but Squid defaults to try the first 10 then give up. To fix add the line: forward_max_tries 25
But where to do so in Endian?

Adding extra squid configuration options in Endian 3:
The Squid config is at /etc/squid/squid.conf – BUT this is rebuild every time you save the web GUI instead to add custom options, add them into /var/efw/proxy/custom.tmpl

For example:
SSH in:
cd /var/efw/proxy/
vi custom.tmpl
[add the following:] forward_max_tries 25

Then resave the settings in the Web gui to force the rebuild of the /etc/squid/squid.conf file.
Then check to see that the settings are there with the following command:
cat /etc/squid/squid.conf
And look for #begin custom.tmpl