Not possible to send emails for Office 365 organisation account

Hi,
I’ve added an organisation account to emClient on PC. After that I imported this to my android cell phone by QR-code. New emails arrive at both devices but sending works only for android mobile! I’ve enabled logging for smtp and got “MailClient.Accounts.AuthenticationAbortedException: Authentifizierung abgebrochen”
Does anybody has an idea?
Best regards
Holger