Append the sender's email signature to outbound emails

[sherifkozman]

Scenario

When a user sends an email from Twenty through a connected Google account (the record composer, the AI send-email tool, or the workflow Send Email action), the email arrives without their signature.

This is because a Gmail signature is applied only by the Gmail web/mobile compose UI — the Gmail API (users.messages.send) does not append it — and Twenty's outbound path has no signature handling. So every email sent from Twenty goes out unsigned, which is a problem for sales/support teams who rely on their work signature (name, title, company, disclaimer) on outbound mail.

Proposed solution

Read the sender's default signature from the Gmail users.settings.sendAs API and append it to the outgoing message, at the single provider-dispatch point (MessagingMessageOutboundService.sendMessage) so all send paths are covered.

• No new OAuth scope — reading sendAs settings is already covered by the gmail.readonly scope connected accounts hold (the existing GoogleEmailAliasManagerService calls the same endpoint).
• Opt-in — gated behind a workspace feature flag (default off).
• Best-effort — a failure to fetch/append never blocks sending.
• Send-only — drafts are excluded (the Gmail compose UI adds the signature when the user opens a draft).

Known limitations / open questions for discussion

• Uses the default signature only — the Gmail API exposes a single signature per send-as address, so Gmail's multiple-signatures (per-context) feature isn't represented. Is that acceptable as a v1?
• Google accounts only initially (Microsoft Graph has an equivalent; IMAP/SMTP would need a stored-signature approach). Worth scoping the multi-provider story here.
• Gating: a workspace flag vs. a per-message-channel toggle vs. a user setting — open to maintainer preference.

Reference implementation

I have a working implementation (verified end-to-end on a self-hosted instance) in #21169 — happy to align it with whatever direction is preferred here before review.

[prastoin]

Hey there, thanks for your feedback !
Lets land on a product direction here before opening any PRs
cc @neo773 @Bonapara

[fraserredmond]

Limitations: "IMAP/SMTP would need a stored-signature approach"

Yes please! We don't use gmail and would like this feature.