Sender IP

the IP address of the originating server.

EHLO domain

The domain name given in the EHLO command MUST be either a primary host name (a domain name that resolves to an address RR) or, if the host has no name, an address literal.

PTR record

A PTR record is a DNS record that resolves an IP address to a domain name as an opposite to what A record does.

A record

An A record resolves a domain name to an IP address as an opposite to what PTR record does.

SPF record

SPF stands for Sender Policy Framework. It is a DNS record of type TXT which specifies a list of senders authorized to send emails on your domain’s behalf. 

TXT Record

TXT record is a type of a DNS recourse record used to associate an arbitrary text with a host.

DKIM

DKIM stands for DomainKeys Identified Mail and it is a protocol which helps organization claim responsibility for an email. It provides a method for validating a domain name associated with an email through the use of cryptography. 

DKIM Signing Domain

This is the domain name identity that has signed the email with their cryptographic signature.

DKIM Selector

The selector is an arbitrary string travelling along with each DKIM signed email which helps the recipient to find the public key in your DNS and validate the DKIM signature. 

DKIM Canonicalization

Canonicalization is a method used by the sender to normalize or standardize the email header and body before signing it with DKIM. Two canonicalization algorithms exist "relaxed" and "simple" for each header and body. The "simple" algorithm tolerates almost no modification and the "relaxed" algorithm tolerates common modifications such as whitespace replacement and header field line rewrapping.

DKIM Signed Headers

This is a complete and ordered list of header fields presented to the signing algorithm.

DKIM Signature

This contains the DKIM signature data of the email.

DKIM signing domain

This is the domain name identity which DKIM signed the email.

DKIM Key Length

This is the size of the DKIM key being used when signing the email. Longer keys are considered stronger and more secure. 

TTL

TTL or time to live is a mechanism that limits the lifespan or lifetime of data in a computer or network

From Domain

This email header displays who the message is from. This is the visible domain shown in your mail client.

Return Path

The email header used to indicate where bounces should be sent in case an email cannot be delivered.
Depending on the mail provider receiving the email an SPF check is either done on this email header first or the EHLO or both.

p=

The p= is a DMARC tag which specifies the policy used. Examples include:

p=none - means no policy will be applied to emails that fail DMARC
p=quarantine - means quarantine emails that fail DMARC
p=reject - means reject emails that fail DMARC.

pct=

The pct= is a DMARC tag which specifies to what percentage of emails the policy should be applied to. If this tag is absent then 100% of the emails will have the policy applied. Other examples:

p=reject; pct=20 means that the specified policy will apply to 20% of the emails, the remaining 80% will have the policy of quarantine applied as this is the next policy down.

p=quarantine; pct=50 means that the specified policy will apply to 50% of the emails, the remaining 50% will have the policy of none applied as this is the next policy down.

p=none; pct=100 means that the specified policy will apply to 100% of the emails.

rua=

The rua= is a DMARC tag which tells the recipient where to send the DMARC aggregate reports to.

ruf=

The rua= is a DMARC tag which tells the recipient where to send the DMARC forensic reports to.

SPF domain

SPF uses the Return-Path/MAIL-FROM domain of emails in order to look up the SPF record of the email sender.

sp=

The sp= is a DMARC tag which specifies the subdomain policy used. 

adkim=

adkim= is a DMARC tag which specifies whether strict or relaxed DKIM alignment mode is required by the Domain Owner.

aspf=

aspf= is a DMARC tag which specifies whether strict or relaxed SPF alignment mode is required by the Domain Owner.

SPF

SPF stands for Sender Policy Framework. It was developed to combat sender address forgery. It is an authentication protocol which verifies the Return-Path/MAIL FROM or HELO/EHLO identities during email transmission.

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