Email Authentication & Deliverability
Learn how cryptographic identity, DNS alignment, recipient consent, and bounce hygiene ensure legitimate emails reach recipient inboxes.
An Honest Reality About Inbox Placement
No email provider can truthfully guarantee "100% inbox placement." Mailbox providers (such as Google, Microsoft, and Yahoo) evaluate hundreds of dynamic factors—including recipient interaction, IP history, domain age, and content filters. Proper authentication (SPF, DKIM, DMARC) proves your identity and prevents spoofing, establishing the foundational trust required for optimal delivery.
The Three Pillars of Email Authentication
Every domain connected to PlusMail is configured with industry-standard cryptographic records that prove message authenticity to receiving mail servers.
Sender Policy Framework
RFC 7208 • IP Authorization
SPF is a DNS TXT record that explicitly specifies which mail servers and IP addresses are authorized to send messages on behalf of your domain name.
Prevents unauthorized spammers from claiming your domain as their return path envelope.
DomainKeys Identified Mail
RFC 6376 • Digital Signature
DKIM attaches a cryptographic digital signature to the email header using an asymmetric key pair. Receiving servers use your public DNS key to verify the message was not altered in transit.
PlusMail provisions 3 separate 2048-bit tokens to enable seamless, zero-downtime key rotation.
Domain-based Reporting
RFC 7489 • Policy Alignment
DMARC connects SPF and DKIM by instructing receiving mailboxes what to do if an incoming email fails authentication: monitor (p=none), quarantine (p=quarantine), or reject (p=reject).
Required by Google and Yahoo since early 2024 for all professional domain senders.
Understanding Email Bounces: Hard vs. Soft
When an email cannot be delivered, the receiving mail server returns a non-delivery report (NDR) with an SMTP status code. Handling these events appropriately is vital to preserving sender reputation:
Hard Bounces (5xx Codes)
Occurs when the recipient address does not exist, the domain is invalid, or the recipient mail server permanently rejects incoming messages.
PlusMail Policy: Hard bounces are instantly placed on our suppression list. No further sending attempts are permitted.
Soft Bounces (4xx Codes)
Occurs when a recipient mailbox is temporarily full, the receiving server is experiencing high load, or a transient network error occurred.
PlusMail Policy: The delivery engine retries automatically using exponential backoff over a 24-hour window before timing out.
Spam Complaints & Feedback Loops (FBL)
When a user clicks "Report as Spam" in Gmail, Outlook, or Yahoo, a complaint notification is sent back to the sending infrastructure through a Feedback Loop.
Major mailbox providers view complaint rates exceeding 0.1% as a strong signal of unsolicited email. PlusMail immediately suppresses any recipient who registers a complaint, ensuring the sender's domain reputation is insulated from future harm.
Transactional vs. Marketing Email Distinction
| Attribute | Transactional Email | Marketing / Bulk Email |
|---|---|---|
| Trigger | User-initiated action (signup, reset, purchase) | Sender-initiated business campaign |
| Content | Personal, unique account details or alerts | Promotional offers, newsletters, announcements |
| Expected Delivery | Sub-second to a few seconds | Batched over hours or days |
| Unsubscribe Requirement | Not legally required (essential service communication) | Mandatory 1-click unsubscribe header & footer link |
| PlusMail Primary Focus | ✓ Supported & Optimized | Strictly regulated (permission required) |
Want to Inspect Your Domain's Readiness?
Our engineers can walk you through automated SPF and DKIM provisioning for your domain.