Sender email address (e.g., [email protected]). After configuring DMARC, SendCloud uses the current domain as the suffix of "from". Also accepts the display-name form "Name [email protected]". Required; empty returns MAIL_FROM_NOTNULL (40801), invalid format returns MAIL_FROM_INCORRECT (40802)

Recipient email addresses (separated by semicolons, e.g., [email protected];[email protected]). Required if not using xsmtpapi or address list; empty returns MAIL_TOS_NOTNULL (40805). Any invalid address returns MAIL_TOS_ERROR (40806); more than 100 addresses returns MAIL_TOS_REACH_MAX (40807). Ignored when xsmtpapi contains a to array or useAddressList=true

Email subject. Required; empty returns MAIL_SUBJECT_NOTNULL (40808); longer than 512 characters returns MAIL_SUBJECT_INCORRECT (40809)

Email content in text/html format. Required if plain is empty; both empty returns MAIL_HTML_PLAIN_NOTEMPTY (40870)

Content summary. Replaces existing summary if present; added if not. Only valid with html

Sender name (shown as "Example customer service [email protected]"). Max 128 characters; malformed returns MAIL_FROMNAME_INCORRECT (40804)

CC addresses (separated by semicolons). Any invalid address returns MAIL_CC_INCORRECT (40853); more than 100 addresses returns MAIL_CCS_REACH_MAX (40854). Ignored when xsmtpapi contains a to array or useAddressList=true

BCC addresses (separated by semicolons). Any invalid address returns MAIL_BCC_INCORRECT (40856); more than 100 addresses returns MAIL_BCCS_REACH_MAX (40857). Ignored when xsmtpapi contains a to array or useAddressList=true

Default reply addresses (separated by semicolons, max 3; exceeding returns MAIL_REPLYTO_SIZE_EXCEED (40879)). Supports plain email or display-name format (e.g., "ASC [email protected]"); invalid address returns MAIL_REPLYTO_INCORRECT (40811). Defaults to "from" if empty or null

Label for this send. Automatically created if not existing in the account. Max length is 255 characters; out-of-range returns LABEL_NAME_FORMATERROR (40105); a name with no letter or digit returns LABEL_NAME_CHARSET_INVALID (40118)

Tags for the request (separated by ";", max 5 tags, each up to 50 characters). More than 5 tags returns GLOBAL_TAGS_MAX (40033); a tag longer than 50 characters or empty returns GLOBAL_TAGS_LENGTH (40034); malformed input returns GLOBAL_TAGS_INCORRECT (40035)

Email headers in JSON format (e.g., {"header1": "value1", "header2": "value2"}). Invalid JSON returns MAIL_HEADERS_INCORRECT (40869)

SMTP extension. See → X-SMTPAPI for details. Invalid JSON or unknown keys (e.g. "substitutions" instead of "sub") return MAIL_XSMTPAPI_ERROR (40817); the to array is capped at 100 (40827). When a to array is present, the to/cc/bcc parameters are ignored. Substitutions use the "sub" key with %var% names, each value list matching the to list length

Email content in text/plain format. Required if html is empty; both empty returns MAIL_HTML_PLAIN_NOTEMPTY (40870)

Max 128 characters; overlong returns GLOBAL_REQUESTID_TOOLONG (40031). Duplicate values within 1 hour (3600s) are only processed once and return GLOBAL_DUPLICATE_REQUEST (40000, "Repeat request") with result=false and no emailIdList

Whether to return emailId. Returns a list for multiple recipients

Whether to enable notification

Whether to use address list (e.g., to=[email protected];[email protected]). When true, to must reference existing address lists: a nonexistent list returns MAIL_ADDRESSLIST_ERROR2 (40863), a malformed list address returns MAIL_ADDRESSLIST_ERROR1 (40862), and more than 5 lists returns MAIL_ADDRESSLIST_REACH_MAX (40864). cc/bcc/xsmtpapi are ignored. On success the task is created asynchronously and statusCode is 40821 with info.maillistTaskId; poll /api/mail/taskinfo for progress

Embedded image ID, which matches the cid value of the src attribute for img tags in email content. For example, for , the value is 123.png. Multiple values are separated by semicolons .If this parameter is used, the email content shall include "<img src='cid:xxxx' /> ".