Require the asynchronous API

[xiexin0606]

This library is really good, much better than vmime and mailcore2.
But when will the asynchronous API is ready? I see it built base on the boost ASIO, it will be easier to support asynchronous API.

Another question: does it thread-safe? Can I use multiple threads to send bulk emails at the same time?

Thanks

[karastojko]

Hi, I plan to add the asynchronous API but after the release of the version 1.0. Currently, I clean some bugs which should make the library more robust.

By taking the last version (commit of few minutes ago), you should be able to use it with a thread per connection. Since there were some corner cases which led to crashes, let me know if you encounter an issue. So far, I tested extensively only with IMAP (plain and SSL), but since the issue was on the TCP level, I expect to work for SMTP without problems.