Because here is main port for Gnus, i writes. According EmacsWiki somewhere, only Mu4e could handle with @outlook.com (smtp.office365.com) amoung Emacs E-mail clients. So i did test with Gnus. Conclusion: Gnus also can handle both smtp.office365.com 587 with starttls. Just i attach two screen shots [1][2]. Thanks, [1] https://gitlab.com/soyeomul/Gnus/blob/master/ss/20200104001.png [2] https://gitlab.com/soyeomul/Gnus/blob/master/ss/20200104001.txt -- ^고맙습니다 _地平天成_ 감사합니다_^))//