I am getting this error message

Spark have advised it is a Microsoft error

Microsoft have advised Windows Live Mail is not longer supported by Microsoft. I have to purchase Microsoft Outlook 2016 to be supported.

We have lots of emails to send but they will not send - will only receive...anyone else struck this?

An unknown error has occurred.

Subject 'Re: Your account is a bit behind.'
Server Error: 554
Server Response: 554 5.7.1 Message rejected due to possible spam content
Windows Live Mail Error ID: 0x800CCC6F
Protocol: SMTP

***Moved from Outlook.com / Email / Sending, receiving, and reading email***