1. What Are The Good Senders List (GSL) Reputation Data Response Codes?

The reputation data response codes – which are published in the Good Senders List (GSL) (also known as our IADB (ISIPP Accreditation Database) files), are a machine readable way for our SuretyMail Email Accreditation program to provide email receiving sites with information, or “data points”, about the legitimacy of the email being sent by the email sender in question.

Specifically, they provide factual information about such things as the level of opt-in, authentication mechanisms published by the sender, how they maintain their mailing lists, and other mailing practices. Taken as a whole, these factual data points paint a picture of the type of email which a receiver can expect to come from the sender, and the sender’s IP addresses.

For example, a data response to a query may reveal that the email sender in question is accredited by us, publishes an SPF record, and builds their mailing lists by confirmed (double) opt-in. Or it may tell the querier that the email coming from the sender’s IP address is all one-to-one email, and not mailing list mail at all, and that they publish rDNS, and SPF. Or it may tell them that the sender is not listed in the IADB database at all (in which case it means that they are not accredited with us).

2. What Are the Data Response Codes, and What Do They Mean?

The data response codes are all in the 127.x.y.z range.

The “x” and “y” value generally indicate the “what” of the data, i.e. what the information provided is, while the “z” value generally indicates the “how much”, or the “if” in the case of a simple “yes/no” data return.

For example, 127.0.255.z is reserved for information about whether the listing is a vouched* listing. In this case ISIPP provides information that a listing is a vouched listing, or that it is not, and so the “z” value indicates simply “yes” or “no”, with “255” being “yes”, and “0” being “no”. (*A vouched listing means that you are either personally known to ISIPP or a referring group, or that your reference and background check and mailing practices demonstrate that you are someone to whom we would refer others for services.)

Another example would be the 127.3.3.z range, which is the level of opt-in for the sender’s mailing lists as reported by the senders themselves (there is another range for externally verified opt-in levels). Again, the “z” value indicates “how much”, with indicating an opt-out policy, indicating that all of the sender’s mailing lists are confirmed opt-in, and values in between indicating an intermediate opt-in level.

Note that there are exceptions to the “z” = “how much” or “yes/no”. In ranges from 127.2.128.z through 127.2.255.z, the “y” indicates a category, and the “z” indicates an affirmative for a subcategory. For example, 127.2.255.z is reserved for information about external authentication systems in which the listee may participate, such as SPF or Ironport’s Bonded Sender. A score of indicates that the sender publishes an SPF record, a score of indicates that the sender is listed with Ironport’s Bonded Sender program.

Confused? It’s ok, these codes are meant for computers to read, but if you really need to know exactly what a given code means, you can look it up on our code list.

3. How Did You Come Up with the Data Response Codes?

ISIPP worked closely with both leading spam filters and ISPs to develop the data response codes. They are based on what ISPs and spam filters need in terms of both data format, and data content.

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