A transactional email has a task to accomplish. The reader may need to confirm an account, find a booking time or identify a payment. A visually impressive layout is not useful if the important action disappears on a small screen or depends on an image loading.
Put the task in the text
Use a clear subject and a short opening that explains why the message arrived. Include the essential reference, date or action as text. Avoid making a decorative image the only place where the information appears.
Use a sensible heading order and descriptive link labels. “View your booking” tells the reader more than several identical “Click here” links. The destination should match the action described, and the application should handle expired or unavailable resources clearly.
Design for constrained reading
Review the message at a narrow width and with enlarged text. Check that long names, references and URLs do not push the layout sideways. Keep text and background contrast strong enough to read comfortably, including around buttons and secondary information.
If an image carries meaning, provide useful alternative text. If it is decorative, avoid repeating information unnecessarily. Leave enough spacing around actions that a reader can select the intended link on a phone.
Keep the plain-text version useful
Sendar's inline message format supports HTML and text content. A plain-text version should preserve the message's essential meaning and links, not just tell the reader to open another client. When the HTML changes, review the text version as part of the same change.
Treat dynamic content as part of the design. Escape user-provided values and test missing optional fields. The production message needs to remain understandable beyond the ideal preview fixture.
Test more than the browser preview
Email clients do not all render HTML the same way. Use representative clients and controlled recipients to inspect the actual message. Check keyboard and assistive-technology use where possible. Keep the final review focused on whether someone can understand and complete the task, rather than whether every visual detail matches the web application.