Letterbook Docs

Auto-response email

Send automatic acknowledgement emails from active inboxes.

Last updated June 25, 2026

What this guide covers#

Auto-response email sends an acknowledgement when customers reach out. It is useful for confirming receipt, setting expectations, and reducing duplicate follow-ups.

Configure it in Settings > Automations > Auto Response Email.

How it works#

Auto-response email is configured per active inbox. Each inbox can have its own acknowledgement content.

Letterbook can send the acknowledgement in two ways:

Mode	Behavior
Reply in Thread	Sends the acknowledgement as a reply in the customer's email thread
Separate email	Sends a new email with its own subject line

Replying in thread is usually the best default because it keeps the acknowledgement attached to the customer's original message. If you disable Reply in Thread, Letterbook shows a subject line field.

The original customer message is automatically quoted below the acknowledgement.

Set it up#

Go to Settings > Automations.
In Auto Response Email, choose the active inbox to configure.
Select Add or Edit.
Choose whether to reply in thread.
Write the acknowledgement body.
If sending as a separate email, set the subject line.
Save.

You can copy an existing auto-response to another active inbox from the inbox action menu.

Available variables#

Auto-response emails support variables in both the body and the subject line when the subject line is shown.

Variable	Meaning
`{{original_subject}}`	The customer's original subject
`{{customer.first_name}}`	Customer first name
`{{customer.last_name}}`	Customer last name
`{{customer.email}}`	Customer email address

The default separate-email subject is Re: {{original_subject}}.

Good acknowledgement copy#

Good auto-responses are short, accurate, and conservative. They should tell the customer that the message was received without promising a resolution time your team cannot meet.

Example:

Hi {{customer.first_name}},

Thanks for reaching out. We received your message and will review it shortly.

If you have more details, you can reply to this thread and they will be added to the same conversation.

Before enabling#

Confirm that: