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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>",
  "ccEmail": "<string>",
  "bccEmail": "<string>",
  "languageCode": "<string>",
  "emailFormat": "<string>",
  "lmx": "<string>",
  "contactPropertiesFallbacks": {},
  "eventPropertiesFallbacks": {},
  "dataVariablesFallbacks": {}
}
'
{
  "id": "cmn5zia4i0017tzli8ric8giv",
  "campaignId": "cln0y4p6r003yl70i1j2k3l4m",
  "subject": "Big spring updates",
  "previewText": "A quick look at what's new",
  "fromName": "Loops",
  "fromEmail": "hello@news.example.com",
  "replyToEmail": "support@example.com",
  "emailFormat": "styled",
  "lmx": "<Paragraph>Hello world</Paragraph>",
  "contentRevisionId": "clv8g2x4z013yl70s9t0u1v2w",
  "updatedAt": "2026-03-28T15:30:00.000Z"
}

​
Request

The campaign or transactional email 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, or the emailMessageContentRevisionId you received when creating the campaign. Used for optimistic concurrency.
​
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.
​
ccEmail
string
CC email address. Requires the team to have CC/BCC enabled.
​
bccEmail
string
BCC email address. Requires the team to have CC/BCC enabled.
​
languageCode
string
Language code for the email. Requires translation to be enabled for the team.
​
emailFormat
string
The rendering format of the email. One of styled or plain.
​
lmx
string
The email body serialized as LMX. Styles must be embedded in the LMX <Style /> tag. The LMX payload must not exceed 100KB.
​
contactPropertiesFallbacks
object
Fallback values for contact properties, keyed by property name. Per-key merge: a string value sets the fallback, a null value deletes it, and keys omitted from the map are left unchanged.
​
eventPropertiesFallbacks
object
Fallback values for event properties, keyed by property name. Per-key merge: a string value sets the fallback, a null value deletes it, and keys omitted from the map are left unchanged.
​
dataVariablesFallbacks
object
Fallback values for data variables, keyed by variable name. Per-key merge: a string value sets the fallback, a null value deletes it, and keys omitted from the map are left unchanged.

​
Response

​
Success

​
id
string
required
​
campaignId
string
Present only when the message belongs to a campaign.
​
transactionalId
string
Present only when the message belongs to a transactional email.
​
subject
string
required
​
previewText
string
required
​
fromName
string
required
​
fromEmail
string
required
​
replyToEmail
string
required
​
ccEmail
string
Only present when set.
​
bccEmail
string
Only present when set.
​
languageCode
string
Only present when set.
​
emailFormat
string
required
One of styled or plain.
​
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
​
contactPropertiesFallbacks
object
Contact property fallbacks. Only present when set.
​
eventPropertiesFallbacks
object
Event property fallbacks. Only present when set.
​
dataVariablesFallbacks
object
Data variable fallbacks. Only present when set.
​
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.
​
message
string
required
{
  "id": "cmn5zia4i0017tzli8ric8giv",
  "campaignId": "cln0y4p6r003yl70i1j2k3l4m",
  "subject": "Big spring updates",
  "previewText": "A quick look at what's new",
  "fromName": "Loops",
  "fromEmail": "hello@news.example.com",
  "replyToEmail": "support@example.com",
  "emailFormat": "styled",
  "lmx": "<Paragraph>Hello world</Paragraph>",
  "contentRevisionId": "clv8g2x4z013yl70s9t0u1v2w",
  "updatedAt": "2026-03-28T15:30:00.000Z"
}
Last modified on June 30, 2026