Not sending emails from office 365 exchange account


I have included various email providers in eM Client. All are working except of office 365 exchange.

We have Exchange Online.
If I include the mailbox as Exchange I get an error that username and password does not fit. Same with automatic setup. IMAP is activated in Exchange.
But it does. It is working well with Teams and OWA.
In this case I have include the mailbox as
For testing I have deleted the GSuite Account because there are issues in Outlook in combination with Exchange. Download of the mails is working but sending delivers the mail in the local folder for outgoing mails and does not send theses mails. I have tested it with different Exchange accounts.

If I include the mailboxes in Outlook 2016/2019 they are recognized as Exchange accounts.

Any suggestions?



It was the Authenticated SMTP Option in Officde 365 Admin Center.