libESMTP is an SMTP client that manages posting (or submission of) electronic mail via a preconfigured MTA.

It may be used as part of a MUA, or other program that must be able to post electronic mail where mail functionality may not be that program's primary purpose.

libESMTP's high-level API shields developers from the complexity of SMTP. It transparently handles many SMTP extensions including authentication, TLS, and PIPELINING for performance. Even without a pipelining server, libESMTP offers much better performance than would be expected from a simple client.