Check domain authentication
- SPF lists approved sending services for the domain.
- DKIM signs messages so receiving systems can verify them.
- DMARC tells receivers how to handle failures and provides reporting when configured correctly.
Review sending behavior
- Avoid sudden bulk campaigns from a normal employee mailbox.
- Remove invalid addresses and stop sending to people who did not request messages.
- Use a reputable campaign platform for newsletters instead of hiding many recipients in BCC.
Keep messages credible
- Use a consistent From address and an honest subject line.
- Balance links and images with clear text and business identification.
- Check the account for compromise if Sent Items contains messages you did not create.
Stop guessing when the problem keeps coming back
Ask for help when authentication records are missing, many providers reject mail, or the domain may have been abused.