Letterbook Docs

Set up forwarding addresses

Forward support mail into Letterbook while keeping your customer-facing email address.

Last updated June 25, 2026

What this guide covers#

Forwarding lets you keep an existing address like support@company.com or help@company.com while routing new support mail into Letterbook.

In this setup, customers still email your normal support address. Your email provider, group, alias, or previous helpdesk forwards a copy of each message to a Letterbook-generated forwarding address. Letterbook then creates a conversation from the forwarded message.

How forwarding works#

Forwarding has three parts:

Customer-facing address: the address customers know, such as support@company.com.
Current mail destination: the place that receives mail today, such as Gmail, Microsoft 365, a Google Group, an alias, or another helpdesk.
Letterbook forwarding address: the generated address Letterbook gives you for inbound routing.

The flow looks like this:

customer -> support@company.com -> current mail provider -> Letterbook forwarding address -> Letterbook conversation

Forwarding is only for receiving inbound messages. If you want Letterbook to send replies from support@company.com, also complete Enable sending from your support address.

Forwarding address versus Gmail integration#

Forwarding and the Gmail integration both get customer email into Letterbook, but they work differently.

Area	Forwarding address	Gmail integration
Provider support	Works with almost any provider that can forward mail	Only for Gmail or Google Workspace mailboxes
Access model	Letterbook receives forwarded messages, but does not need direct mailbox access	Letterbook connects directly to the Google mailbox
Setup owner	Whoever can edit forwarding rules	Whoever can authorize the Gmail mailbox, plus admin approval if required
Good fit	Aliases, groups, shared addresses, previous helpdesks, non-Gmail providers	Dedicated Gmail or Google Workspace support inboxes
Common risk	Forwarding loops, sender rewriting, duplicate routes	Google authorization or Workspace admin approval issues

Use forwarding when you want the most flexible routing option or when the address customers email is not a dedicated Gmail mailbox.

Use the Gmail integration when the support inbox is a Google mailbox and you want a direct connection through Google instead of maintaining forwarding rules.

When to use forwarding#

Forwarding is a good choice when:

Your support email is hosted outside Gmail.
Your support address is a group, alias, or distribution list.
You are migrating from another helpdesk and want new messages to flow into Letterbook.
You want to avoid granting direct mailbox access.
You need to route multiple customer-facing addresses into the same Letterbook inbox.
You want to receive mail in Letterbook before outbound sending is fully verified.

Forwarding is also useful during migration. You can route new mail into Letterbook while keeping the old mailbox available for historical tickets until the transition is complete.

Setup steps#

Open the inbox or email channel settings in Letterbook.
Create or copy the Letterbook forwarding address.
Open the system that currently receives mail for your support address.
Add a forwarding rule from your support address to the Letterbook forwarding address.
Confirm any verification email your provider sends.
Send a test email from an external address that looks like a real customer.
Confirm the conversation appears in Letterbook.
Check that the customer email, subject, body, and attachments are preserved.
Disable old auto-replies, helpdesk triggers, or duplicate forwarding paths that could double-reply.

What to test before going live#

Send realistic test messages, not just a one-word test email.

Check that:

The conversation appears in the correct Letterbook inbox.
The customer email is the original sender, not your forwarding address.
The subject line is preserved.
The body is readable and not wrapped in a forwarded-message block.
Attachments arrive correctly.
Replies thread back into the same conversation.
The old mailbox or helpdesk is not also replying.

Multiple support addresses#

You can forward more than one customer-facing address into Letterbook. For example, a team might forward:

support@company.com
help@company.com
billing@company.com
security@company.com

When using multiple addresses, decide whether they should all land in the same inbox or whether some should route to a separate team or priority. Test each address separately because aliases, groups, and mailboxes can have different forwarding behavior.

Forwarding from groups, aliases, and shared mailboxes#

Groups, aliases, and shared mailboxes often behave differently from a normal mailbox login.

Check:

Whether the address can forward to an external destination.
Whether an admin must approve external forwarding.
Whether the original customer sender is preserved.
Whether replies from Letterbook go back to the customer instead of the group.
Whether the group or shared mailbox sends its own auto-reply.

If the provider rewrites the sender or wraps the original email as an attachment, try a different forwarding mode or use a dedicated mailbox route.

Avoid forwarding loops#

A forwarding loop happens when two systems send the same message back and forth.

Common causes:

Letterbook forwards or replies to a mailbox that forwards back into Letterbook.
A previous helpdesk still forwards incoming tickets after Letterbook is live.
An auto-reply from the old mailbox creates a new incoming email.
A distribution list includes the same support address that forwards to Letterbook.

Before launch, remove old routing rules that are no longer needed and send a test message to confirm only one Letterbook conversation is created.

Provider notes#

Gmail and Google Workspace usually send a verification email before forwarding is enabled.
Microsoft 365 and Outlook may require an admin to allow external forwarding.
Previous helpdesks should stop receiving new forwarded tickets before Letterbook becomes the primary queue.
DNS-hosted forwarding services can work, but test sender preservation before using them in production.
Catch-all and alias addresses should be tested with real customer-style messages.

Troubleshooting#

Forwarding verification email did not arrive#

Some providers require the destination address to confirm forwarding. Check Letterbook for the verification email or code. If the provider asks for a code, copy it from the forwarded message and complete setup in the provider.

Messages show the forwarding mailbox instead of the customer#

The provider may be rewriting the sender. Look for a forwarding option that preserves the original sender and message headers. Avoid forwarding as an attachment unless your provider has no other option.

Attachments are missing#

Check attachment size limits in the original provider and any previous helpdesk in the route. Send another test with a small attachment and a larger attachment to confirm the behavior.

Threading is split across multiple conversations#

Threading can split if the subject or message headers change during forwarding. Check whether the forwarding system adds prefixes, rewrites subjects, or sends new messages instead of forwarding the original email.

Both Letterbook and the old inbox are sending replies#

Disable auto-replies, macros, automations, and agent replies in the old inbox before going live. During migration, choose one system as the source of truth for new tickets.

Customers receive duplicate replies#

Check for multiple active routes into Letterbook and multiple systems replying. Duplicates usually come from one mailbox forwarding to two destinations, or from both a Gmail integration and forwarding rule being active for the same address.