Answer 1

I don't think C standard lib have any function to do that ( because of obvious reasons )
You can either "abuse" your system's command processor to send mail via "sendmail" in your C program using system(), Or much better, look for a library that do the job for you.
P.S.
Make sure to read "why system() is evil", before planning to use it in your program.
https://www.cplusplus.com/forum/articles/11153/