E-mails remain in the outbox

I have a problem that half of my emails are sent and half remain in the outbox and I don’t have any solution.Any solution?

If it is a Microsoft account, it might be what is being discussed here: Can receive email but unable to send

Has anyone managed to solve the issue with e mails (hotmail) not sending using eM Client?
This has just started happening.
I can receive but not send. I can send when not using eM Client.

It throws me these 2 types of errors

[SMTP] Cannot send message (Email body not accepted due to the following reason:
"5.2.0 STOREDRV.Submission.Exception:OutboundSpamException; Failed to process message due to a permanent exception with message [BeginDiagnosticData]WASCL UserAction verdict is not None. Actual verdict is RefuseQuota. OutboundSpamException: WASCL UserAction verdict is not None. Actual verdict is RefuseQuota.[EndDiagnosticData]

[IMAP] Known Microsoft Exchange server error “User is authenticated but not connected.” has been encountered on IMAP connection. This issue is temporary and should be automatically resolved by the server. If not, please contact your mail provider.