Curl_easy_perform() failed: Unsupported protocol

I’m using wp7608 module and Developer studio.Im trying to send a mail by using this code
maill.c (2.5 KB)
(this code build successfully in developer studio ,but
I try to run this code ,Im getting this error curl_easy_perform() failed: Unsupported protocol

But in curl smtp,smtps protocol are enabled

root@swi-mdm9x28-wp:~# curl -V
curl 7.61.0 (arm-poky-linux-gnueabi) libcurl/7.61.0 OpenSSL/1.0.2p zlib/1.2.11 libssh2/1.8.0
Release-Date: 2018-07-11
Protocols: file ftp ftps http https scp sftp smtp smtps
Features: AsynchDNS IPv6 Largefile NTLM NTLM_WB SSL libz TLS-SRP UnixSockets HTTPS-proxy
.Please tell how to slove this problem