Domain-based Message Authentication, Reporting, and Conformance, or DMARC, is a technical standard that helps protect email senders and recipients from spam, spoofing, and phishing.
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了解 DMARC
Domain-based Message Authentication, Reporting, and Conformance, or DMARC, is a technical standard that helps protect email senders and recipients from spam, spoofing, and phishing. DMARC allows an organization to publish a policy that defines its 电子邮件认证 practices and provides instructions to receiving mail servers for how to enforce them. In this edition of “DMARC Explained” you’ll learn what DMARC is and how it works.
Specifically, DMARC establishes a method for a domain owner to:
公布电子邮件验证做法
State what actions should be taken on mail that fails authentication checks
允许报告对声称来自其域的邮件所采取的这些行动
DMARC itself is not itself an email authentication protocol, but it builds on key authentication standards SPF and DKIM. With them, it supplements SMTP, the basic protocol used to send email, because SMTP does not itself include any mechanisms for implementing or defining policies for email authentication.
DMARC 如何工作？
DMARC relies on the established SPF and DKIM standards for email authentication. It also piggybacks on the well-established Domain Name System (DNS). In general terms, the process of DMARC validation works like this:
A domain administrator publishes the policy defining its email authentication practices and how receiving mail servers should handle mail that violates this policy. This DMARC policy is listed as part of the domain’s overall DNS records.
When an inbound mail server receives an incoming email, it uses DNS to look up the DMARC policy for the domain contained in the message’s “From” (RFC 5322) header. ǞǞǞ inbound server then checks evaluates the message for three key factors:
Does the message’s DKIM signature validate?
邮件是否来自发送域 SPF 记录允许的 IP 地址？
Do the headers in the message show proper “domain alignment”?
With this information, the server is ready to apply the sending domain’s DMARC policy to decide whether to accept, reject, or otherwise flag the email message.
After using DMARC policy to determine the proper disposition for the message, the receiving mail server will report the outcome to the sending domain owner.
什么是 DMARC 记录？
A DMARC record is included in an organization’s DNS database. An DMARC record is a specially-formatted version of a standard DNS TXT record with a particular name, namely “_dmarc.mydomain.com” (note the leading underscore). A DMARC record looks something like this: _dmarc.mydomain.com. IN TXT “v=DMARC1\; p=none\; rua=mailto:dmarc-aggregate@mydomain.com\; ruf=mailto:dmarc-afrf@mydomain.com\; pct=100”
用简单的英语从左到右读，这张唱片是这样写的
v=DMARC1 specifies the DMARC version
p=none specifies the preferred treatment, or DMARC policy
rua=mailto:dmarc-aggregate@mydomain.com is the mailbox to which aggregate reports should be sent
ruf=mailto:dmarc-afrf@mydomain.com is the mailbox to which forensic reports should be sent
pct=100 is the percentage of mail to which the domain owner would like to have its policy applied
Additional configuration options are available for a domain owner to use in its DMARC policy record as well, but these are the basics.
DMARC 域对齐是什么意思？
“Domain alignment” is a concept in DMARC that expands the domain validation intrinsic to SPF and DKIM. DMARC domain alignment matches a message’s “from” domain with information relevant to these other standards:
对于 SPF，报文的发件人域和返回路径域必须匹配
For DKIM, the message’s From domain and its DKIM d= domain must match
ǞǞǞ alignment can be relaxed (matching base domains, but allowing different subdomains) or strict (precisely matching the entire domain). This choice is specified in the published DMARC policy of the sending domain.
什么是 DMARC p= 策略？
The DMARC specification provides three choices for domain owners to use to specify their preferred treatment of mail that fails DMARC validation checks. These “p= policies” are:
none: treat the mail the same as it would be without any DMARC validation
隔离： accept the mail but place it somewhere other than the recipient’s inbox (typically the spam folder)
拒绝： reject the message outright
Remember that the domain owner can only request, not force, enforcement of its DMARC record; it’s up 到 inbound mail server to decide whether or not to honor the requested policy.
什么是 DMARC 报告？
DMARC reports are generated by inbound mail servers as part of the DMARC validation process. There are two formats of DMARC reports:
汇总报告, which are XML documents showing statistical data about the messages received that claimed to be from a particular domain. Date reported includes authentication results and message disposition. Aggregate reports are designed to be machine-readable.
法医报告, which are individual copies of messages which failed authentication, each enclosed in a full email message using a special format called AFRF. Forensic report can be useful both for troubleshooting a domain’s own authentication issues and for identifying malicious domains and web sites.
DMARC 与 SPF、DKIM 或其他标准有什么关系？
DKIM、SPF 和 DMARC 都是支持电子邮件身份验证不同方面的标准。它们解决的问题互为补充。
SPF allows senders to define which IP addresses are allowed to send mail for a particular domain.
DKIM provides an encryption key and digital signature that verifies that an email message was not faked or altered.
DMARC unifies the SPF and DKIM authentication mechanisms into a common framework and allows domain owners to declare how they would like email from that domain to be handled if it fails an authorization test.
我需要 DMARC 吗？
If you are a business sending commercial or transactional email, you definitely need to implement one or more forms of email authentication to verify that an email is actually from you or your business. Properly configuring DMARC helps receiving mail servers determine how to evaluate messages that claim to be from your domain, and it is one of the most important steps you can take to improve your deliverability.
However, standards like DMARC only go so far; MessageBird and other email experts recommend implementing a DMARC email authentication policy in context of a complete messaging strategy.