Hi,
There's no definitive documented answer in regards to the maximum number of conferences. Microsoft do advise on the maximum amount of participants in a single conference, so using that number (250) in combination with the Microsoft user models you can give
yourself an idea of maximum number of conferences.
The below article is one of a couple that have already done this maths;
http://windowsitpro.com/lync/lync-server-2013-conferencing-limits
Although without even doing this calculation I would suggest the 400 conferences is absolutely WAY above what you should be running on a single standard edition server.
Kind regards
Ben
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