There are several potential reasons for Microsoft delivery issues. Here's how to diagnose and fix them:

1. First, check your metrics in Email Signals:

• If your bounce rate is above 2%, you'll need to clean your lists

• If spam complaints are above 0.1%, review your content and opt-in practices

• Look at your delayed rates to Microsoft domains

• Check Message Events for specific Microsoft bounce codes

• [optional with Inbox Tracker] Review reputation using SNDS or GPT

2. Next, review any recent changes:

• Have you sent more email than usual?

• Did you change your email content?

• Are you mailing to new lists?

• Did you modify your authentication settings?

3. To resolve the issue:

• Verify your authentication (SPF, DKIM, DMARC) in Email's Domains section

• Remove inactive subscribers (no engagement for 6+ months)

• Stop sending to bounced addresses

• Process unsubscribes immediately

• Keep your sending volume consistent

• Include clear unsubscribe links

• Use clear subject lines

• Include your physical mailing address

Contact Email Support if:

• You've completed all these steps

• Your metrics are within normal ranges

• Issues continue for more than 48 hours

• You see unusual bounce codes

• You need SNDS data for your dedicated IPs

Most blocks clear automatically within 24-48 hours if you follow good sending practices.