Email clients

The page is a collection of resources for email client developers in order to help architecting, implementing, and maintaining support for structured email.

More low level software libraries are discussed on a dedicated page.


Based on the generic motivation for structured email, the following points might be highlighted in the particular case of email client software:

  • As indicated by the past “extension” of email client software to deal with address books, calendars, tasks, notes or files, email clients can be considered a central hub between users email interaction with persons and organizations and their core personal data
  • Besides for calendars, interaction of email data with those different applications is often ad hoc and very heterogeneous when comparing different email clients

Data extraction


Data usage

Display as cards

A common usage of structured data in email is to provide simple visual summaries (“cards”) of data and provide simple access to eventual further actions and processing.

Contextual highlighting

Structured data can not just replace human message reading by automation, but may also be used to improve the reading experience by combinining/augmenting human readable content with additional metadata derived from structured data.


Some vendors may store extracted structured data independently of the original email for fast access. For instance, Gmail mentions that structured data might be included in personal search results and Google Assistant actions.

This may likely be a future area of standardization.

Vacation notices

A structured email use case which might directly benefit the core functionality of email clients are structured vacation notices. See use cases for more detail.


Structured email, as a more general and holistic approach, allows to consider the reconcilation of related concepts, which over time might have been architecturally scattered throughout an email client implementation.

Client- vs. server-side processing

Several current features of email are not well aligned with today’s practice of operating multiple email clients on top of an email server. This includes:

  • Calendar invite processing
  • Email filtering

Special email interaction

Over time, several cases for special user interaction with emails have been surfacing - mostly based on corresponding specific RFCs. This includes:

  • Calendar invite processing (“accept”, “reject”)
  • Message Delivery Notifications (“read receipts”)
  • Mailing list unsubscribe

Security and trust

Many email clients define and maintain a self-defined model of trust in which the user can state which email senders are trustworthy. A common application scenario for this is the display of “remote images” embedded in HTML emails (see also here).

Special-use email attachments