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Message: <blockquote data-quote="dhoremans" data-source="post: 1608528" data-attributes="member: 333967">I can have only one window (message or box) open at one time while in Mail. When I want to have a look at inbox or another message I will have to close the message that I am writing or reading. The  problem has not always been there. It appeared around a year ago. But I do not remember what did change in the environment. I am not aware that I did change any setting. Please advise solution, many thanks in advance. DirkOS X/iOS version: 10.9.5Software involved with the issue: Mail OS XVersion number of the software involved: N/APiece(s) of hardware involved: Mac AirError message(s): None</blockquote>