simple-java-mail

Add ability to use custom MimeMessage implementation (e.g. to override the default Message-ID generation strategy)

fixed Java version back to 1.7

finished release-4.2.2

#73: always close down connection pool when finished sending all *known* async emails (later emails will run with a completely new connection pool)

updated *all* dependency versions and got rid of the ie-shim for ie9 support