City of Largo Institutes New Email SPAM Procedures

March 11, 2007

This was recently posted to the City’s website:


Problems Sending Email to

The City of Largo has implemented a new SPAM appliance that blocks electronic mail based on one of three criteria: 1) The message is checked for viruses. If the message contains a virus it is moved offline for our review.2) Reverse and forward DNS are checked on the address that sent your email message. Similar to Caller ID on a telephone, this is a way to determine if your mail is really coming from where it says it is, and is not coming from a faked address.

If you aren’t sure if this is configured correctly on your side, you will need to contact your ISP (Internet Service Provider) or internal IT department.

The following is a technical description for your ISP/IT staff:

    Example of Forward and Reverse DNS: For instance the IP address that Largo uses to send out email is That IP resolves to “” (Reverse DNS). “” resolves to (Forward DNS). Use tools such as “nslookup” to validate that your Internet records are correct.Email that doesn’t have both forward and reverse DNS is rejected and sent back to the sender. 99% of such email is SPAM.

3) Email is checked for content. The SPAM appliance checks for construction methods and word content that seem to be similar to SPAM. If you are sure your DNS records are correct and the message are still being returned, then something in your message appears “SPAM-like” to the appliance. The best technique is to eliminate your tagline/signatures and make the messages as simple as can be. Sending text messages instead of richer text (like HTML) will increase the chances of the message successfully being allowed into the City.


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