Mailguard E-mail Filtering Service
What it Does
Our e-mail filtering service uses several techniques to detect and discard spam messages:
- Reject e-mail from known spam sources using blacklisted server databases
- Reject e-mail containing common spam and pornographic keywords or keyphrases listed in a spam phrase database
- Reject e-mail messages that are contained in a database of collected spam messages
- Examine e-mail for spam characteristics and reject or flag messages that are considered likely spam
Our experience has been that these techniques will eliminate 95% or more of the spam received with very few "false positives" (classifying legitimate e-mail as spam).
How it Works
Your e-mail is directed to our filtering mail server. Each message is then filtered according to the following criteria:
- We first check the mail source against a real-time database
of known spam sources (blacklists). If the message originates
from a blacklisted server, the message is rejected by our
We utilize several online real-time blacklists as well as proprietary blacklists that we maintain.
- The sender's e-mail address
domain is checked for participation in SPF.
SPF is an IP address-based "Sender Permitted" authorization protocol. SPF allows a domain
owner to publish a list of permitted servers. This will greatly
reduce the acceptance of forged e-mail sender addresses. If
the domain owner participates in SPF, and the sending server is
authorized, the message is passed to the next stage. If the
domain owner participates in SPF, and the sending server is not
authorized, the message is rejected. If the domain owner
does not participate in SPF, no action is taken at this stage.
- The message is checked for a variety of obvious spam or pornographic
keywords or keyphrases listed in a database that is maintained
by Tela. The message is also compared to a real-time database
of confirmed spam messages. (Razor2). The message is rejected
if it is found in either database.
- The message and attachments
are examined for common characteristics found in spam. Once
the entire message has been examined, the message is assigned
a quantitative measurement based on the characteristics found.
See Spam Assassin.org for
more information on these characteristics.
The mesage is classified as spam if the spam level exceeds your spam classification threshold. The default threshold (5 points) will classify most unwanted e-mail as spam and minimize the number of false positives. The message is flagged with the spam level.
- You may choose to have e-mail which exceeds the default spam threshold
passed through to your mailbox for processing by your own e-mail
rules", or we can discard the message. Messages passed through
contain a "SpamStatus" and "SpamLevel" that
can be used to process the message by your e-mail client.
- The message is then screened by our virus scanner and quarantined if a virus is detected.
The message is then delivered to your mailbox if it has not been discarded or quarantined.
If you have your own SMTP server, we can filter your e-mail on our server. We then will forward the e-mail to your SMTP server after tagging it with the spam level. Messages classified as spam can also be dropped as above. No changes are necessary on your e-mail server to use the SMTP forwarding. Your primary MX record should point to our e-mail server to route the incoming mail through our mail filtering server.
We can also configure an additional filter for SMTP forwarding to reject messages that are sent to non-existent mailboxes. Many spammers send messages to obsolete e-mail addresses or use a "baby book" attack whereby they send e-mail to many names at a domain (firstname.lastname@example.org, email@example.com, etc.). We can discard these messages early in the processing, before they pass through the above filters. This way these messages will never reach your server. You will need to provide a current list of valid e-mail addresses for this option.
The cost is $2.00/month per mailbox for email spam and antivirus filtering. Quantity discounts are available for larger organizations.
If you have an e-mail account with another ISP, we can filter your e-mail. We will set up a mailbox on our server that will retrieve mail every 10 minutes from your current ISP using POP. This e-mail is then passed through our e-mail filters above and deposited into a POP mailbox on our server. You then retrieve your e-mail using POP from our server. Your e-mail address will not change.
The cost is $5.00/month per mailbox which includes the POP retrieval, spam filtering, and virus screening.