Definition
Email authentication protocols are a set of technical standards that allow mailbox providers to verify that an email was sent by an authorised sender and was not altered in transit. The main protocols are SPF, DKIM, DMARC and BIMI.
SPF, or Sender Policy Framework, lists the IP addresses and servers authorised to send email for a domain. DKIM, or DomainKeys Identified Mail, adds a cryptographic signature that proves the message was not modified. DMARC, or Domain-based Message Authentication, Reporting and Conformance, tells receivers how to handle messages that fail SPF or DKIM checks and provides reporting back to the sender.
BIMI, or Brand Indicators for Message Identification, builds on DMARC by displaying a brand logo next to authenticated emails in supported clients. Together, these protocols protect recipients from phishing, improve deliverability and increase brand recognition.
Best Practices
- Set up SPF, DKIM and DMARC for every domain that sends email.
- Start DMARC with a 'p=none' policy, then move to 'p=quarantine' and finally 'p=reject.'
- Monitor DMARC reports to identify unauthorised senders using your domain.
- Keep DNS records updated when you change email service providers or add sending infrastructure.
- Use BIMI only after DMARC is enforced at 'p=quarantine' or 'p=reject.'
Related Glossary Terms
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Management
Bounce management is the process of handling emails that are rejected by mailbox providers, including classification, removal of bad addresses and protection of sender reputation.
Bounce Rate Threshold
A bounce rate threshold is the percentage of hard or soft bounces at which email platforms and ISPs begin to penalise sender reputation, typically around 2-5%.
Frequently Asked Questions
SPF, DKIM, DMARC and BIMI are the most common. SPF authorises servers, DKIM verifies integrity, DMARC sets handling policy and BIMI displays brand logos.
SPF, DKIM and DMARC are strongly recommended. BIMI is optional and requires a verified mark certificate for most implementations.
Yes. Proper authentication builds trust with mailbox providers and reduces the chance of being filtered as spam or phishing.
The mailbox provider follows the DMARC policy. 'p=none' takes no action, 'p=quarantine' sends to spam and 'p=reject' blocks the message.
Use DNS lookup tools, DMARC report analysers or your email service provider's authentication dashboard to verify records.