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POST
/
v1
/
email-messages
/
{emailMessageId}
Update an email message
curl --request POST \
  --url https://app.loops.so/api/v1/email-messages/{emailMessageId} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "expectedRevisionId": "<string>",
  "subject": "<string>",
  "previewText": "<string>",
  "fromName": "<string>",
  "fromEmail": "<string>",
  "replyToEmail": "<string>",
  "lmx": "<string>"
}
'
{
  "success": true,
  "emailMessageId": "em_01hxyz",
  "campaignId": "cmp_01hxyz",
  "subject": "Big spring updates",
  "previewText": "A quick look at what's new",
  "fromName": "Loops",
  "fromEmail": "hello@news.example.com",
  "replyToEmail": "support@example.com",
  "lmx": "<Email><Text>Hello world</Text></Email>",
  "contentRevisionId": "rev_01hyza",
  "updatedAt": "2026-03-28T15:30:00.000Z"
}

Documentation Index

Fetch the complete documentation index at: https://loops.so/docs/llms.txt

Use this file to discover all available pages before exploring further.

Content API endpoints are currently in an open alpha and are subject to change.

​
Request

The campaign that owns this email message must be in Draft status.

​
Path parameters

​
emailMessageId
string
required
The ID of the email message.

​
Body

​
expectedRevisionId
string
The contentRevisionId you last fetched. Used for optimistic concurrency. The request is rejected with 409 Conflict if the server’s revision has advanced.
​
subject
string
Email subject line.
​
previewText
string
Email preview text.
​
fromName
string
Sender display name.
​
fromEmail
string
The sender username (without @ or domain). The team’s sending domain is appended automatically.
​
replyToEmail
string
Reply-to email. Must be empty or a valid email address.
​
lmx
string
The email body serialized as LMX. Styles must be embedded in the LMX <Style /> tag. The LMX payload must not exceed 100KB.

​
Response

​
Success

​
success
boolean
required
​
emailMessageId
string
required
​
campaignId
nullable string
required
​
subject
string
required
​
previewText
string
required
​
fromName
string
required
​
fromEmail
string
required
​
replyToEmail
string
required
​
lmx
string
required
​
contentRevisionId
nullable string
required
The current content revision ID. Use this value as expectedRevisionId on your next update request.
​
updatedAt
string
required
​
warnings
object[]
Non-fatal issues raised while compiling the submitted LMX. Only present on update responses when warnings were produced.

​
Error

If the request body is invalid, a 400 Bad Request is returned. A 404 Not Found is returned if the email message does not exist. A 409 Conflict is returned when the campaign is not in draft status, when contentRevisionId is stale, when content cannot be parsed, or when the email message uses MJML format. A 413 Payload Too Large is returned when the LMX payload exceeds the 100KB limit. A 422 Unprocessable Entity is returned when LMX compilation fails. If the API key is invalid (or content API is not enabled for your team), a 401 Unauthorized is returned.
​
success
boolean
required
​
message
string
required
{
  "success": true,
  "emailMessageId": "em_01hxyz",
  "campaignId": "cmp_01hxyz",
  "subject": "Big spring updates",
  "previewText": "A quick look at what's new",
  "fromName": "Loops",
  "fromEmail": "hello@news.example.com",
  "replyToEmail": "support@example.com",
  "lmx": "<Email><Text>Hello world</Text></Email>",
  "contentRevisionId": "rev_01hyza",
  "updatedAt": "2026-03-28T15:30:00.000Z"
}
Last modified on May 20, 2026