CURLOPT_MAIL_AUTH(3) Library Functions Manual CURLOPT_MAIL_AUTH(3)
NAME
CURLOPT_MAIL_AUTH - SMTP authentication address
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MAIL_AUTH, char *auth);
DESCRIPTION
Pass a pointer to a null-terminated string as parameter. This is used
to specify the authentication address (identity) of a submitted message
that is being relayed to another server.
This optional parameter allows co-operating agents in a trusted
environment to communicate the authentication of individual messages
and should only be used by the application program, using libcurl, if
the application is itself a mail server acting in such an environment.
If the application is operating as such and the AUTH address is not
known or is invalid, then an empty string should be used for this
parameter.
Unlike CURLOPT_MAIL_FROM(3) and CURLOPT_MAIL_RCPT(3), the address
should not be specified within a pair of angled brackets (<>). If an
empty string is used, a pair of brackets is sent by libcurl as required
by RFC 2554.
The application does not have to keep the string around after setting
this option.
Using this option multiple times makes the last set string override the
previous ones. Set it to NULL to disable its use again.
DEFAULT
NULL
PROTOCOLS
This functionality affects smtp only
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
curl_easy_setopt(curl, CURLOPT_URL, "smtp://example.com/");
curl_easy_setopt(curl, CURLOPT_MAIL_AUTH, "<secret@cave>");
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
AVAILABILITY
Added in curl 7.25.0
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_MAIL_FROM(3), CURLOPT_MAIL_RCPT(3)
libcurl 2026-03-23 CURLOPT_MAIL_AUTH(3)
curl 8.19.0 - Generated Fri Mar 27 15:28:52 CDT 2026