Modern email library

[Ben Rubinstein]

I've one app that's been in existence for over a decade, which uses Shao 
Sean's libSmtp. It works fine.

Now I find myself wanting to send email from a new stack I'm working on. I 
could just drag that library out again, but I suspect that a more modern way 
is to use tsNet.

AFAICT tsNet handles the protocol of communicating with the server to transmit 
a message (i.e. the SMTP part), but doesn't offer any assistance with putting 
the message together (formatting with attachments etc).

What do modern people use for this? Obviously I could rip the relevant parts 
out of libSMTP; or I recall that Sarah Reichelt had a library; is there a 
default answer among those who've sent email in the last ten years?

TIA,

Ben