Email sending error

[Johumber]

For the past 2 days I have been unable to send any emails, receiving them is fine. Error reads "Your message couldn't be delivered because you weren't recognized as a valid sender. The most common reason for this is that your email address is suspected of sending spam and it's no longer allowed to send email. Contact your email admin for assistance."  Any ideas?

[#2]

Did you contact your IT folks? They have a way for checking and unlisting the account, depending on the situation: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/removing-user-from-restr...

In case the IP itself is blocked: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/use-the-delist-portal-to...

[#3]

Unfortunately as a sole trader consultant I don’t have anyone! However I have had a successful call with Microsoft and all is now resolved. Thanks!

[#4]

@Johumber355 kindly assist with steps.