Your emails can land into spam box due to following reasons:
- Removal of SPF record
- Bad domain or custom envelope reputation
Every recipient server is different and may apply different spam filtering criteria for the messages being received. In most cases, recipient servers don’t provide any information about spam filtering to the sender of an email that was filtered. It would give too much information to spammers who would use that data to get around spam filters.
Spam filters are constantly changing to adapt to new techniques and types of spam messages, so what lands in the inbox today could be spam filtered tomorrow. There are some things you can do to help ensure your emails are being delivered to the inbox.
Most of the major email providers, including Gmail, Yahoo!, Hotmail use engagement-based filtering to help detect spam. This means that the more your recipients interact with your emails, the more highly engaged your audience is, and the more likely your emails land in recipients inboxes. The possibility of email landing in spam folders increases when a lot of users are marking your emails as spam. If you succeed in moving your majot chunk of emails out of the spam folder then it’s a positive sign of getting your future emails delivered in recipients inbox.