Greylisting
9th December 2005
We have added another very important feature to our email server configuration - Greylisting. This new shielding method blocks out huge amounts of spam!
Greylisting allows your email server to delay delivery of email from unknown servers. However, it only does this if the unknown server also happens to be misconfigured.
Normally, the other server will try again later, and the email will then be delivered to you. This is where spammers lose out, because most spamming software will not bother to try again later.
A greylisting configuration is now shipped by default with the Lemon email server package. This new package is only available with the Debian Sarge release. If your servers aren't using this version yet, it could be time to upgrade!
SPF (Sender Policy Framework)
9th December 2005
SPF fights return-path address forgery and makes it easier to identify spoofs. In simple language, SPF makes it easy for the owner of a domain to say:
"I will only ever send email from these servers"
This means that when anybody else sees mail that claims to be from you, but is not coming from one of your servers, they know that it is a fake. SPF aims to prevent spammers from ruining other peoples reputations.
So, there are two parts to SPF; publishing your information, and checking other people's when you receive mail that claims to be from them.
- Publishing
- Say you own my-domain.com. You add an SPF record containing a list of your outgoing mail servers to the DNS information for my-domain.com. Then, when they receive a mail that claims to be from someone@my-domain.com, other servers will be able to check it against the list you published. If the mail is not coming from a server on that list, they will know that it is a fake.
- Checking
- Again, say you own my-domain.com, and your incoming mailserver is configured to check SPF records. When it receives a message that claims to be from other-domain.com, it will look up other-domain.com's SPF information. If the server that it is receiving the message from is in the SPF list, it will deliver the mail as normal. If not, in the configuration we use, the mail will be rejected.
An SPF check, as described above, is now included in our email server configurations. This should help protect against "phishing" attacks and also prevent some spam.
Lemon Web Filtering
9th December 2005
Lemon Web Filtering filters out potentially malicious content from websites before they are passed to the browser.
It works in conjunction with "squid", which you may already be using as a web proxy. It seems this breaks many websites (particularly those that do not conform to recognised web standards), so it also includes a facility to exclude sites by domain and/or ip-address from being filtered.
If it sounds like this could be useful, please give us a call.
Lemon Wall
9th December 2005
An overview of the Lemon firewalls...
- Single external IP, multiple IPs on LAN
- make ftp work through nat -> ftp-proxy
- make smtp/pop3 work for internal/external ip
- queues to queue SYN/ACK and ssh differently
Gizmo
9th December 2005
As their website says (www.gizmoproject.com), Gizmo is a free phone for your computer. It uses a simple interface to set up phone calls on your PC.
If you call other Gizmo users, the call is free. You also have access to voicemail and conference calls, and there are add-ons that allow you make and receive calls from any mobile phone or landline.
If you've heard of Skype, and this sounds similar, that's because it is. The difference is that Gizmo will interoperate with other systems, so you're not just stuck on the one network.
.eu Domains
9th December 2005
New domains are going to be made available from January 2006.
They end in ".eu", so for example a Lemon Computing url would be:
http://www.lemon-computing.eu
Applying for these new domains involves a two stage process.
- The first stage is for applications from Trademark holders, and runs from 6th to the 28th January 2006.
- The second stage is for Companies, and runs from 29 January 2006. Individuals can apply from March 2006.
However, there is a lot of paper work involved with the application, so if you are interested in this you need to consider your application now.
The Lemon PBX
9th December 2005
The LemonPBX is a robust and unique switchboard system based on the "Asterisk" software package. It is suitable for small to medium companies (2-50 users).
The PBX has a rich feature set, including:
- Callcentre-style queuing
- Caller ID
- Internal transfers
- Transfers to external numbers (e.g. mobiles)
- Voicemail
- PIN number access (e.g. priority support lines)
- Grouping of phones (e.g. one call rings multiple phones)
- A highly customisable call flow and routing system
It uses only industry standards, thus it is compatible with a variety of other software, including
- IAXCOMM, Microsoft Messenger as a user interface for making calls
- PostgreSQL, MySQL and Microsoft SQL Server for call routing, resolving of phone numbers to names, and accounting
All communications are based on TCP/IP, the standard used on the internet. The preferred protocol on top of TCP/IP is SIP, which is a form of VoIP.
That makes it compatible out of the box with www.gizmoproject.com/. It thereby provides the option of transparently locating telephones in remote locations. Any phone can be connected to the PBX via the internet. Combine with our LemonVPN for a complete home-worker solution.
It can connect to the outside world via:
- BT ISDN2e
- BT ISDN30
- VoIP (SIP) carriers
- PSTN (using the SipuraSPA3000)
It also features an (optional) graphical interface for receptionists, showing the current use of lines/phones and status of queues.
Exim4 Lemon Config
9th December 2005
Overview
This is a debian package that configures many features and aspects of exim4. It includes support for rigid anti-spam-measures and many useful tools. It has been designed with robustness in mind, including a protection against mis-configuration by administrators or users.
Detail
This package out-of-the-box provides
- strict DNS checks on senders (forward/reverse) (with greylisting,)
- upper limit of 25MB per email.
- handles multiple domains (dozens and more) on the same server
- rejection of spam based on rules of spamhaus.
and optionally
- option of authenticated smtp
- option of screening incoming and outgoing email
- optionally maintains a copy of your sent items on the server if your email client cannot do this (e.g. Microsoft Outlook) (only if mail is sent via this server of course)
- custom, sophisticated rules using procmail
- automatic delivery of spam into spam folders rather than your inbox
- spam-assassin based rulesets
- live virus scanning of emails via clamav (free) or sophos (3rd party license)
and best of all... it works nicely with our prefered choice of imap server: courier and our (not quite so preferred but still useful) package: usertools
Invoice Queries
9th December 2005
Via Email
If you have a query about an item on our invoice, please send an email to invoice@lemon-computing.com stating the invoice number and your query. If you have a query on a particular workhour item, please state the workhour number as well, which is the number in [brackets] on the timesheet.
Via Telephone
If you do need to call us for technical support, you can call the number 020 8878 2138, and ask the operator for the credit control department. This number is for non-contract clients.
