Update DMARC-how-to.md

DMARC-how-to.md

@@ -4,12 +4,40 @@
 This how-to is created by the Dutch Internet Standards Platform (the organization behind [internet.nl](https://internet.nl)) and is meant to provide practical information and guidance on implementing DMARC.
 
 # What is DMARC?
-DMARC is short for **D**omain based **M**essage **A**uthentication, **R**eporting and **C**onformance and is described in [RFC 7489](https://tools.ietf.org/html/rfc7489). With DMARC the owner of a domain can, by means of a DNS record, publish a  policy that states how to handle e-mail which is not properly authenticated using SPF and/or DKIM. At the same time it provides the means for receiving reports which allows a domain's administrator to detect whether their domainname is used for phishing or spam.
+DMARC is short for **D**omain based **M**essage **A**uthentication, **R**eporting and **C**onformance and is described in [RFC 7489](https://tools.ietf.org/html/rfc7489). With DMARC the owner of a domain can, by means of a DNS record, publish a  policy that states how to handle e-mail (deliver, quarantine, reject) which is not properly authenticated using SPF and/or DKIM. 
+
+At the same time DMARC also provides the means for receiving reports which allows a domain's administrator to detect whether their domainname is used for phishing or spam. 
+
  
 # Why use DMARC?
-to-do.
+Before DMARC, organizations already took several measures to determine the authenticity of an e-mail (like SPF and DKIM) to reduce the received amount of SPAM to a minimum. This is basically a good thing, but if these measures fail to choose whether or not an email is SPAM with a high level of certainty, the choice is redirected to the addressee (receiving party). This methodology is prone to abuse, since users are generally not equiped with the knowledge and/or means to classify incoming emails. 
+ 
+DMARC addresses this problem and enables the owner of a domain to take explicit responsiblity with regard to the actions taken by the sending party when the validity of an incoming email cannot be determined.  
 
 # Tips, tricks and notices for implementation
 * Interoperabily issues: https://tools.ietf.org/html/rfc7960
 * DMARC does not require both DKIM or SPF. 
-* 
+* Parked domain: “DMARC p=reject”. Make sure to include rua and ruf addresses, since this allows monitoring of possible abuse attempts.
+* RFC 7489 [states](https://tools.ietf.org/html/rfc7489#section-6.4) that the tags dmarc-version ("v=") and dmarc-request ("p=") should be on the first and second position of the DMARC record. The order of the other tags does not matter: "components other than dmarc-version and dmarc-request may appear in any order".
+* [Errata 5440 of RFC 7489](https://www.rfc-editor.org/errata_search.php?rfc=7489) states that a semicolon should be included in the DMARC version tag. Correct: "v=DMARC1;". Incorrect: "v=DMARC1". 
+
+# Creating a DMARC record
+The DMARC policy is published by means of DNS TXT record.
+Overview 
+
+rua: aggregate reports
+ruf: forensic reports
+
+| DMARC configuration tag | Required? | Value(s) | Explanation |
+| ---  | --- |  --- | --- |
+| v | mandatory | DMARC1; | |
+| p | mandatory | none<br>quaritine<br>reject | |
+| rua | optional | rua@example.nl | This field contains an e-mail address |
+| ruf | optional |ruf@example.nl | This field contains an e-mail address |
+| fo | mandatory | 0<br>1<br>s<br>d | reporting oprions for |
+| adkim | optional | s<br>r | |
+| aspf | optional | s<br>r | |
+| pct | optional | | |
+| rf | optional | | |
+| ri | optional | | |
+| sp | optional | | |