Here are some things to consider when troubleshooting email delivery delays in Exchange:

1. Check Exchange logs for errors.
2. Ensure the most up-to-date version of Exchange is being used.
3. Check routing tables for correct configuration.
4. Make sure there is proper firewall and security configurations.
5. Check user account settings.
6. Check for any mail flow delivery rules are configured.
7. Check DNS and MX records are correct.