Custom email signatures

Save one signature per mailbox and let Inkbox add it to outgoing email. Custom signatures are available on paid plans. Each mailbox has its own content and on/off setting, so agents can sign with different names and contact details. A signature is part of the email body, not an attachment. You do not need a signature file to use one.

API access

Use an admin API key to manage signatures for mailboxes in your organization. Use a claimed agent’s identity-scoped API key to manage that agent’s own mailbox. An agent-scoped key cannot change another agent’s signature. Both use PATCH /api/v1/mail/mailboxes/{email_address} and the same SDK or CLI commands below. The organization must have access to custom signatures to save content or enable insertion. Disabling or clearing remains available without it.

Set up in the Console

Open your mailbox’s Mailbox settings in the Inkbox Console, then choose Signature. You can open these settings from the Email mailbox list or the identity’s inbox. Click your saved signature or Add signature to open the editor. Choose Text or HTML, then edit the content or import a file. Choose Save to apply your changes. Clicking outside the editor shows a preview without saving; click the signature again to keep editing your draft. Turn automatic insertion on or off, then choose Save. Turning it off keeps the saved content. The organization’s Email footer setting is separate from this mailbox setting.

Choose a format

Format	What to provide
Plain text	A name, role, contact details, and full URLs as ordinary text.
HTML	An HTML fragment with basic formatting, links, optional tables, and a logo. Provide a text equivalent for plain-text messages, or let Inkbox generate one.
`.txt` or plain-text `.sig`	Read the file as text and use its contents as `signature_text`. The extension does not change the email format.
`.html` or `.htm`	Read the file as text and use its contents as `signature_html`. Use the signature fragment rather than a complete webpage.

.sig is not one universal file format. If a mail app exported a proprietary signature package, first export or copy its plain text or HTML. Inkbox does not parse signature packages or attach signature files to messages. Each text or HTML value can contain up to 16,384 characters. For a logo, use an absolute HTTPS image URL such as https://example.com/logo.png and include helpful alt text. Images are linked, not uploaded or attached; recipients’ mail apps may require permission to display them. Local paths, relative URLs, and embedded image references are not supported. Inkbox normalizes HTML to supported email formatting before saving. Read the returned HTML to see the saved result. The generated text fallback contains readable text, not necessarily the destination URLs of links; supply your own text value if those URLs should appear in plain-text email.

Configure through the SDK or CLI

Use version 0.7.1 or later of the Python SDK, TypeScript SDK, or CLI. These examples save both formats and enable automatic insertion.

from inkbox import Inkbox

inkbox = Inkbox(api_key="YOUR_API_KEY")
mailbox = inkbox.mailboxes.update(
    "agent@inkboxmail.com",
    signature_html="<p><strong>Example Support</strong><br>example.com</p>",
    signature_text="Example Support\nexample.com",
    signature_enabled=True,
)
print(mailbox.signature_html)

import { Inkbox } from "@inkbox/sdk";

const inkbox = new Inkbox({ apiKey: "YOUR_API_KEY" });
const mailbox = await inkbox.mailboxes.update("agent@inkboxmail.com", {
  signatureHtml: "<p><strong>Example Support</strong><br>example.com</p>",
  signatureText: "Example Support\nexample.com",
  signatureEnabled: true,
});
console.log(mailbox.signatureHtml);

inkbox mailbox update agent@inkboxmail.com \
  --signature-html '<p><strong>Example Support</strong><br>example.com</p>' \
  --signature-text 'Example Support — example.com' \
  --signature-enabled

Use an admin API key or a claimed agent’s key for its own mailbox. See Update mailbox for the REST equivalent and complete request and response fields.

Read a signature from a file

The CLI reads the file and submits its contents. It does not attach the file.

CLI

inkbox mailbox update agent@inkboxmail.com \
  --signature-html-file signature.html \
  --signature-text-file signature.sig \
  --signature-enabled

Use only one content option per format: inline value, file, or clear. You can combine an HTML option with a text option.

Turn insertion off or clear content

Disable automatic insertion without losing either format:

CLI

inkbox mailbox update agent@inkboxmail.com --no-signature-enabled

Clear both saved formats and disable insertion:

CLI

inkbox mailbox update agent@inkboxmail.com \
  --clear-signature-html --clear-signature-text --no-signature-enabled

For SDK requests, use None in Python or null in TypeScript to clear a format. Use False or false for the enabled setting. Omit a field to preserve it.

Understand updates and fallbacks

New mailboxes start with both formats null and signature_enabled: false.
Updating HTML without a text field regenerates the text fallback. Clearing HTML without a text field also clears the saved text.
Supply both fields when you want your own text fallback. A null text field still falls back to readable text from saved HTML at send time.
To switch from HTML to text only, explicitly clear HTML and provide text in the same update.
Empty or whitespace-only strings clear a format. An enabled signature with no content adds nothing.
A logo-only HTML signature still appears in the HTML version. If it has no readable text, the plain-text version contains only your message content.

The API rejects signature_enabled: null; omit the field to keep the current setting. Saving nonempty content or enabling insertion without feature access returns 402. Disabling or clearing remains available. An admin can check signature availability before showing configuration controls.

What recipients receive

Inkbox applies the current enabled signature to new messages, replies, reply-all, forwards, draft sends, and SMTP submissions, when your organization has access to custom signatures. An HTML signature adds an HTML version to a text-only message. Recipients receive the formatted signature, including its images and links, with a plain-text fallback. Inkbox escapes your plain-text message when creating the HTML version. This does not enable open tracking. If you supply an HTML body, Inkbox preserves its formatting and inserts the signature into it. Messages with both versions receive a signature in each. A text-only signature does not turn a text-only message into HTML; it is formatted as text when inserted into an existing HTML body. The signature appears after your new content and before recognized quoted history. If Inkbox does not recognize a mail app’s quote format, it appends the signature to the body. Attachments and original messages forwarded as attachments are unchanged. Saved drafts do not have a signature inserted automatically. They use the mailbox’s current signature when sent. Already composed delivery retries keep the original signature, so later edits do not change sent history or add another signature to that retry. Do not manually add the same signature to each message. If your mail app adds one locally, turn off that local signature or turn off Inkbox’s automatic insertion to avoid duplicates. Signed or encrypted SMTP message bodies require automatic custom signature insertion and the Inkbox branding footer to be disabled before sending. These are independent controls:

Control	Scope	Effect
`signature_enabled`	One mailbox	Adds your saved custom signature when the feature is available.
`remove_branding_footer`	Organization	Removes Sent via Inkbox on paid plans when set to `true`.

When both appear, your custom signature comes before the Inkbox footer. Enabling a signature never removes the footer. Disabling a signature never restores or removes it. See Billing settings to change the footer. If your organization loses access to custom signatures, Inkbox retains the saved content and enabled preference but stops inserting it. Insertion resumes when access is restored, unless you disabled the mailbox setting.

Get started

Capabilities

API keys

MCP

Webhooks

Signing keys

Skills

Integrations

Custom email signatures

API access

Set up in the Console

Choose a format

Configure through the SDK or CLI

Read a signature from a file

Turn insertion off or clear content

Understand updates and fallbacks

What recipients receive

Signatures and the Inkbox footer

​API access

​Set up in the Console

​Choose a format

​Configure through the SDK or CLI

​Read a signature from a file

​Turn insertion off or clear content

​Understand updates and fallbacks

​What recipients receive

​Signatures and the Inkbox footer

API access

Set up in the Console

Choose a format

Configure through the SDK or CLI

Read a signature from a file

Turn insertion off or clear content

Understand updates and fallbacks

What recipients receive

Signatures and the Inkbox footer