Our outbound mail filters very carefully analyze dozens of attributes before determining whether a message is considered spam or not, and all decisions are based entirely on recipient feedback. When email users anywhere mark a received message as spam, that feedback goes to mail hosts globally who pool their data with CloudMark and determine commonalities between flagged messages to determine how to identify spam going forward. This is why it is crucial not to send any advertising mail that others might block as spam.
Our outbound mail filters have a threshold for "spammy" content - and if a sender's outgoing messages exceed this threshold, their account will be prevented from sending messages containing spammy content for a consecutive period of 24 hours. After 24 consecutive hours without an attempt to send spammy content, the block will be lifted and users will be able to send normally, but the filtering continues. If users exceed the outgoing threshold for spammy content, accounts will be flagged again.
I know this can be an inconvenience, but it is absolutely necessary for us to maintain a solid reputation for the domain as an entity and continue to host mail for hundreds of thousands of users.
With the way spam filtering is moving globally, if we do not do the above, a single abusing user (intentional or non intentional) can cause a domain name to be blacklisted and this would affect all the users.
I hope this explanation helps allow you to continue to use our services successfully.
It is very important to also share the following email with your email users:
One thing to remember is that if the users are using client-side email application such as Microsoft Outlook, and the messages are landing in the "Junk E-Mail" folder and not simply the"Spam" folder, then that is the email client's own built-in spam filter and is not related to our server-side spam filtering. We recommend that you disable the Outlook / mail client built in spam filter and rely on your EnsureMail /Exchange filtering.
If the spam is going to the "Spam" folder, then we can investigate and resolve by moving these emails to a new folder that we want you to create in webmail or OWA ( False Positives)
With this information, we can certainly work towards a better end-user experience.