Mailguard E-mail Filtering Service

Tela offers e-mail filtering to greatly reduce the amount of unsolicited e-mail (spam) to your mail account or server. Tela also employs server-based antivirus to trap any e-mail-borne viruses. Our e-mail filtering works with e-mail accounts on our server (local mailboxes) or on your e-mail server (SMTP forwarding). We also offer filtering of mailboxes stored at other ISPs (POP Forwarding). There is no additional software that you need to buy or install with this 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:

  1. 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 server. We utilize several online real-time blacklists as well as proprietary blacklists that we maintain.

  2. 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.

  3. 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.

  4. The message and attachments are examined for common characteristics found in spam. Once the entire message has been examined, the message is assigned a "spam level", a quantitative measurement based on the characteristics found. See Spam 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.

  5. 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 client "inbox 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.

  6. 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.

SMTP Forwarding

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 (,, 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.

POP Forwarding

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.