What could your Spam folder be containing
Have you ever sent an email to someone and they didn't receive it ?
Friends or email correspondents report that your emails are marked as spam or they receive unsolicited emails from you or even say that your emails never reach them.
Antispam services use the reputation of domains, IP addresses and email addresses to detect if it sent spam at some point. If the reputation is low, meaning that there is some suspicious activity associated with one of them, then there is a danger that the emails sent from that domain/email address will be marked as spam. Actually, depending on the configuration of the filter, the emails might be even delayed, moved to spam folder or even not delivered at all.
The best way to prevent something like this to happen to your email address and domain is to regularly monitor who accessed your account and keep a close look on the “Sent items” to see if there is something sent without your approval. However, if someone hacked your account or got your credentials from a website hacked (could even be your email provider), then they probably use an API to send emails on your behalf. In this case, you will probably not see anything in “Sent Items”.
No matter how this happened, the solutions are always the same:
Change your password
enable two-factor authentication in order to be asked when someone or something accesses to your account.
Inform the email provider about what happened and ask for guidance