Email domain rewriting for enterprises
Extend your email domain
across every org.
PostMerge rewrites email domains in transit across M365 and Google Workspace tenants, so your merged organization presents a unified brand to the world — from day one.
The Problem
Email domain lock-in
Microsoft 365 and Google Workspace each restrict a domain to a single tenant. After a merger, you're stuck with a fragmented brand and no easy path forward.
Risky domain migrations
Moving users to a new tenant is expensive, disruptive, and takes months — all while your brand looks fractured to clients.
Mismatched sender domains
Employees on the acquired company's tenant keep sending from @acquiredco.com, confusing clients, vendors, and partners.
Staggered rebrand rollout
Without a rewriting layer, you wait months before any org-wide email rebrand takes effect — if it ever happens cleanly.
The Solution
Set your email domains free.
PostMerge sits between your tenants and the internet as a transparent rewriting layer. Every outbound message is intercepted, all domain references rewritten to your unified brand, re-signed with DKIM, and delivered — without touching the original tenant configuration.
No tenant migration. No IT downtime. No waiting. Your users send from their existing mailboxes and the world sees one brand.
See all features →Before — leaves acquiredco tenant
After — delivered to internet
The PostMerge Promise
Rebrand on Day 1.
Not after a long migration. Not after months of IT work. Day one.
Unified brand instantly
Every outbound email from every tenant looks like it comes from one company — the day you flip the switch.
Zero tenant disruption
No mailbox migrations. No DNS cutover chaos. Users keep their existing accounts and send from their usual clients.
Setup in minutes
Point your outbound connector to PostMerge, upload your domain mappings, verify DNS records, and go live.
What you won't need with PostMerge:
How It Works
Simple. Powerful. Secure.
Simple
A single outbound connector change in M365 or Google Workspace is all it takes to route mail through PostMerge. No agent installations. No complex DNS rerouting.
Powerful
Full header rewriting (From, Reply-To, Message-ID, References), ICS calendar attachment rewriting, DKIM re-signing, per-sender overrides, and inbound reverse rewrite for replies.
Secure
DKIM keys stored in AWS KMS. TLS everywhere. Multi-AZ redundancy. Full audit trail for every rewrite. SOC 2 compliant infrastructure.
Get Started
Up and running in 5 steps.
Sign up and create your organization
Create a PostMerge account and configure your unified brand domain (e.g. newbrand.com).
Add your tenant domains
Register each source domain (e.g. acquiredco.com) that should be rewritten to the unified domain.
Configure outbound connectors
In M365 or Google Workspace, add a connector that routes outbound mail through your PostMerge relay endpoint.
Verify DNS records
Add SPF, DKIM, and DMARC records for your unified domain. The portal validates everything before go-live.
Enable rewriting and go live
Flip the switch. Every outbound email from every tenant is immediately rewritten and delivered under your unified brand.
Present one brand.
From day one.
No migrations. No contracts. Just a unified email brand across every tenant, immediately.
14-day free trial · No credit card required