Sending offline HTML

[André]

I'm newbie to OpenEMM, facing an issue in mailings with offline HTML through the web interface.
It seems to be a very basic issue, but I have tried all the steps that are given in the user manual, and all I can get is mailing with in-line HTML.
My mailing has the mail format "Text, HTML and Offline-HTML" and there are text modules in HTML version. My test distribution list have only test recipients with offline HTML mailing format.
I've tried using <img src=""> tag, [agnIMAGE name=""] tag and the insert image button on the OpenEMM HTML editor (that also results in <img src> tag). All of them results in fine in-line HTML for several email clients tested (outlook, thunderbird, webmail).
I didn't find any clue at wiki, FAQ, video tutorials, forum or website search.
Please, help me in this regard.