Kosh Blog

We cover topics related to custom domain email, mailbox infrastructure, security, and deliverability.

auth_inspect.log
DKIM Warning: Key < 2048 bits

d=company.com s=k1 1024-bit RSA

Upgraded to Kosh 2048-bit ED25519
May 10, 2026•4 min read
DeliverabilityDNSSecurity

Email Deliverability PSA: 1024-bit DKIM keys are being flagged by major inboxes

Google, Yahoo, and Microsoft have tightened sender authentication thresholds. Domains still signing with legacy 1024-bit RSA keys are experiencing degraded spam scores. Here is what changed and how Kosh automatically deploys rotating 2048-bit DKIM keys.

Parminder Singh

Parminder Singh

Founder & Architect, Kosh

IMAP Stream Sync100% Synced
Google Workspace → Kosh42,890 msgs

Zero dropped packets • MX cutover verified

Apr 28, 2026•6 min read
ArchitectureIMAPZero-Downtime

Migrating 100,000+ mailboxes from Google Workspace without dropping a single email

How we engineered a streaming IMAP synchronization pipeline that preserves message hierarchies, migrates attachments in parallel, and verifies DNS cutover without duplicate UID propagation.

Parminder Singh

Parminder Singh

Founder & Architect, Kosh

Annual Cost Comparison (20 users)
Traditional Provider$1,680/yr
Kosh Flat Workspace$468/yr
Apr 14, 2026•5 min read
EconomicsStartupsPricing

The hidden tax of per-seat email: Why team communication shouldn't scale linearly with head count

Legacy enterprise suites penalize fast-growing startups by charging $7 to $18 per month for every single inbox, contractor, or shared alias. We break down the actual infrastructure cost of operating high-reputation mail systems.

Parminder Singh

Parminder Singh

Founder & Architect, Kosh

Zero-Access Envelope

CIPHER: AES-256-GCM

KEY_EXCHANGE: X25519_P256

KOSH_SERVER_ACCESS: ZERO

Mar 30, 2026•5 min read
PrivacyZero-AccessCryptography

Zero-access mailbox architecture: How Kosh ensures we can never read your emails

A technical walkthrough of client-envelope encryption, public-key storage isolation, and why modern email platforms should never train machine learning models on your team's customer conversations.

Parminder Singh

Parminder Singh

Founder & Architect, Kosh

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