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IMHO space can be called special character but it looks like SmarterMail is not taking it as one of them. One of my clients which where creating new mailbox tried to use password where he used special character but SmarterMail reported that his password does not met password requirements with error "Password does not meet password requirements: a symbol". When he has changed space to other special character it worked. So my question is does space is or it is not a special character? According to w3.org it is:
but can someone from SmarterTools devs check this problem?