1/ is it possible to send offline messages with the web messenger?
This feature is not supported right now.
2/ is there an API to send online-, offline-messages from outside the messenger?
No.
3/ when appears a release with this features?
We will do our best to finish it in our new product Date Chat. But I am not sure how long it will take.
asp.net Chat http://cutesoft.net/ASP.NET+Chat/default.aspx
Web Messenger: http://cutesoft.net/Web-Messenger/default.aspx
asp.net wysiwyg editor: http://cutesoft.net/ASP.NET+WYSIWYG+Editor/default.aspx
asp wysiwyg html editor: http://cutesoft.net/ASP
asp.net Image Gallery: http://cutesoft.net/ASP.NET+Image+Gallery/default.aspx
Live Support: http://cutesoft.net/live-support/default.aspx