Client-Side Email Signature

A client-side email signature is installed in the user's email client (Outlook desktop, Outlook web, Gmail, Apple Mail, mobile mail apps) so that the signature is visible during compose and is saved in the user's Sent Items folder. The user can see and edit the signature before sending. Implementation differs by client. For Outlook on Microsoft 365, an Outlook add-in is the most reliable approach because it supports Outlook desktop, Outlook on the web, and Outlook mobile. For Gmail on Google Workspace, the Gmail API can write directly to each user's signature settings via OAuth. For Apple Mail and other native clients, client-side installation typically requires per-device setup or configuration profiles. Client-side signatures are the right choice when users need to see signatures before sending, when multiple signature variants must be user-selectable, or when the signature includes interactive elements that depend on user choice. The trade-off is that signatures only appear when the user sends from a configured client, so server-side stamping is often layered on top as a backstop.