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https://nishantrana.me/2012/07/11/system-argumentexception-the-specified-string-is-not-in-the-form-required-for-a-subject-error-while-sending-mail-through-plugin-in-crm-2011/
“System.ArgumentException: The specified string is not in the form required for a subject” error while sending mail through plugin in CRM 2011