Mimecast Greylisting

If emails are being delayed, blocked, or not appearing in Mimecast message tracking, this can be caused by Mimecast Greylisting.

Even when a sender or domain is added to Permitted Senders, Greylisting may still evaluate and defer messages.

To ensure reliable delivery, sending domains and IP addresses must also be added to the Greylisting bypass/ignore list.

When to Use This Guide

Use this guidance if:

• Emails are delayed or not arriving.
• Emails do not appear in Mimecast message tracking.
• Sender/domain is already permitted, but delivery issues persist.

Bypass Greylisting for a Sender

1. Log in to the Mimecast Admin Portal.
2. Navigate to: Gateway → Policies → Greylisting
3. Edit the active Greylisting policy.
4. Add the required sending domains and IP addresses to the Ignore / Bypass / Excluded Senders list.
5. Save changes.
6. Wait 5-10 minutes and send a test email.

Recommended Configuration

Ensure the following are configured:

• Sender domain added to Permitted Senders
• Sender domain added to Greylisting bypass/ignore
• Sending IP addresses added to Greylisting bypass/ignore

All three should be present for consistent delivery.

Verification

After updating Greylisting:

• Test email is delivered successfully.
• Message appears in Mimecast logs as Accepted.
• No further deferrals related to Greylisting.