Apache commons Net

Apache commons net is a library for client side for many internet protocols. some of the main protocols supported are

1. FTP
2. SMTP/POP3
3. IMAP
4. TELNET
5. WHOIS
6. FINGER

An example on how to send an email through this library can be found in this post.

http://www.javacodegeeks.com/2013/11/sending-a-mail-in-java-and-android-with-apache-commons-net-smtp-starttls-ssl.html