Using MTL ยป Computation

E-mail Spam Filtering

Overview

IMPORTANT NOTE: If you forward your MTL e-mail to your MIT e-mail account, then please read no further. Instead, you need to refer to MIT's instructions on how to enable spam filtering.

In order to curb the ever increasing amounts of spam that MTL users get in their MTL INBOXes, MTL has implemented spam filtering/tagging of suspicious e-mails. After an e-mail has run through the MTL message scanning service , it will be put through the MTL spam tagging service and be tagged with a spam score if it is found to be possibly suspicious. This score is not a number but a sequence of 's'es where the higher number of 's'es means that the message has a higher probability of being spam or junk e-mail. This spam score is attached to the header of each possible spam message. Users can then opt for the MTL mail server to redirect messages that exceed a certain MTL spam threshold to a special spam filter folder (this folder is called mtl-spam-filter) in their IMAP folders directory. Please see the next section on how to set your MTL spam threshold.

Enabling/Disabling Spam Filtering

You can now change your MTL Spam settings on-line by going to MUMMS and logging in. Once there you can click on 'View Your E-mail Settings' in order to view/change your current MTL e-mail settings.

Spam Scoring and Settings

As mentioned above in the Overview section, the MTL spam tagging service adds a header to each e-mail that it suspects to be possible spam or suspicious. This header line contains a sequence of 's'es where the higher number of 's'es means that the message has a higher probability of being spam or junk e-mail. So, when you set your MTL spam threshold level, the higher the number you choose, the less aggressive your spam filtering will be. If you choose a lower number, then the more aggressive the filtering will be. For example, if you choose a Custom Setting of '7', then any e-mail with spam headers that contain a sequence of 7 or more 's'es will be filtered into your mtl-spam-filter IMAP folder. If you don't understand what all of this means then it is highly recommended that you accept the default setting of 'Medium' when you set up your MTL spam filtering. If you then decide that this is either too aggressive or too lax, you can always go back and change either setting.

Effectiveness of Spam Filtering

What and what is not spam is very hard to determine and can sometimes be a personal preference. This means that it is inevitable that some spam will get through even the most sophisticated filtering mechanism. If you have turned on filtering but are still getting a lot of spam messages in your INBOX, then you can try to increase either spam filtering threshold if it is currently set to a lower score threshold (e.g. if your current setting is 9, you can try and raise your setting to 6). While raising your spam filtering level may capture more spam, it may also increase the number of legitimate e-mails that are mistakenly marked as spam. Please see the next question regarding the downside to setting the score threshold to an overly aggressive level. MTL will continue to try and improve the spam filtering capabilities in order to increase the effectiveness of the spam filtering and to minimize the chances of false positives which are described in the next section.

False Positives and MTL Spam Filtering

What and what is not spam is very hard to determine and can sometimes be a personal preference. This means that it is possible that some legitimate e-mail may get mistakenly put into your MTL spam filter folder even by the most sophisticated filtering mechanism. If you have turned on filtering and are getting legitimate e-mails being placed into your mtl-spam-filter folder, then you can try to decrease your spam filtering level if it is currently set to a high (i.e. aggressive) score threshold (e.g. if your current setting is 6, you can try and raise your setting to 9). While lowering your spam filtering level may eliminate the possibility of legitimate e-mail being mistakenly put into your mtl-spam-filterfolder, it may also increase the number of spam e-mails that end up in your INBOX. No matter what you have your spam filtering level set to, it is highly recommended and strongly encouraged that you make sure to check your mtl-spam-filter folder on a daily (or other frequent) basis, checking for any false positives (legitimate e-mail) that got filtered and deleting anything that you know is junk/spam. Please see the section below regarding automatic purging of e-mail from people's MTL spam filter folders. MTL will continue to try and improve the spam filtering capabilities in order to increase the effectiveness of the spam filtering and to minimize the chances of false positives. If you are getting persistent false positives from a legitimate sender, please see the section below on blacklists/whitelists.

POP and MTL Spam Filtering

The short answer is yes. The long answer is that while the MTL spam filtering can be set up and will work, because of the use of POP instead of IMAP, you will have no way to view the contents of your mtl-spam-filter folder. This is very important since it is possible that some of your legitimate e-mail could be mistakenly put into the mtl-spam-filter folder and you will have no way of checking the contents of that folder. The easiest solution to this problem is to switch your mail client to use IMAP instead of POP and this is the recommended solution. If you'd still like to continue to use POP, then please see the section below on spam headers and filtering Using your e-mail client software and not the server side MTL spam filtering. If you have questions about this, then you should send an e-mail to mail-problems@mtl.mit.edu and someone will be able to answer your questions.

Automatic Purging of MTL Spam Folder Messages

Because MTL currently does not have any e-mail quota limits thus allowing users to store as much e-mail as they want on the MTL mail server, it is necessary to make sure that people's mtl-spam-filter folders do not grow without bound. In order to deal with this, messages older than 30 days will be automatically purged from all mtl-spam-filter folders. So, if you have MTL spam filtering enabled, it is highly recommended and strongly encouraged that you make sure to check your mtl-spam-filter folder on a daily (or other frequent) basis, checking for any false positives (legitimate e-mail) that got filtered and deleting anything that you know is junk/spam.

Forwarding E-mail and MTL Spam Filtering

If you currently forward your e-mail from MTL to another address, then you can't take advantage of the MTL spam filtering into the mtl-spam-filter folder. But you can still take advantage of the spam tagging that is taking place on every message that goes in and out of the MTL mail server. Please see the section below for more details on how to do this.

MTL Spam Header Information

If you would like to do your own filtering within each of your e-mail clients instead of Using the automatic MTL server side filtering, then make sure to disable your MTL Spam Filter setting. You will then need to set up your e-mail clients in order to do their own filtering. The specific header information you will need to search for within your e-mail client's filtering mechanism are the following:

MTL's Header Line: X-MTL-MailServer-SpamScore: ss....

where you choose the number of 's'es to filter on. The lower the number of 's'es, the more aggressive the spam filtering will be. For example, if you want to filter out all e-mail that gets a spam score of 6 or higher, then you should set up your e-mail client to filter out e-mail with the following line in its header information:

MTL's Header Line: X-MTL-MailServer-SpamScore: ssssss

Good Senders/Bad Senders

Good Sender lists (or whitelists) are lists of addresses that a user wants to receive e-mail regardless of whether or not it may be spam. Bad Sender lists (or blacklists) are lists of addresses that a user wants marked as spam regardless of whether or not it really is spam. You can now manage your MTL Good/Bad Sender lists on-line by going to MUMMS and logging in. Once there you can click on 'View Your E-mail Settings' in order to view/change your current MTL e-mail settings including Good/Bad Sender lists. It is important to realize though that mail header information can be forged and it can be hard to tell where e-mail is coming from - thus blacklisting a certain e-mail address may not prove effective in stopping the spam since spammers can forge where their mail is coming from.

Computation

MTL Annual Research Report 2017: View Online