HTML vs plain text: compare the actual MIME message

Define the decision

A message can look like plain text while still being sent as HTML. Zintara’s reviewed campaign sending path constructs an HTML body; removing formatting in the editor does not by itself create a separate text/plain alternative.

Work through the procedure

1. Export a controlled received message and inspect Content-Type.
2. Check whether the MIME structure includes text/plain, text/html or both.
3. Review legibility, links and fallback behavior in the actual receiving client.
4. Compare content variants without claiming a MIME change the application does not make.

Worked example

The following is a synthetic example for this procedure, not a customer result or performance benchmark.

Editor appearance: a few unformatted sentences
Received MIME: text/html
Correct label: simple HTML email
Incorrect label: verified multipart alternative with a plain-text part

Read the result

The distinction matters when documenting deliverability tests. A visual comparison cannot establish which MIME structure was used, and a MIME choice alone does not explain every filtering outcome.

Check before moving on

1. Test the exact sending path used by the campaign.
2. Inspect attachments separately because they change the MIME structure.

Limits and next action

Do not promise that plain text always outperforms HTML. If a true alternative body is a requirement, verify that capability in the deployed sender before relying on it.

Source: Zintara campaign format context