This can happen when your mail account has been compromised and a spammer has gained access to your account.

Once an account has been identified as sending spam, it is blocked as it has serious consequences to the whole mail platform for all users.

To have the account cleared the user is requested to run a scan for Virus and/or Malware and change their password to something more secure.

Once this is done all we can do is request for the users to be removed from the block-list, however this is a request to a 3rd party, which can take time.