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Internal Emails Blocked by Anti-Spam Filters

Author: Luis Fernandes Updated

Summary

Internal E-Mails are flagged as inbound and blocked by spam filters

Overview

MailEssentials recognizes internal emails as inbound when it's not installed on the Exchange server (non Edge).
The Anti-Spam module is designed to only listen on and scan Inbound SMTP traffic. When internal emails (sent from and to same domain) are blocked, one of the below is true: 
  • Email is an auto-generated notification and is sent from a server, network device or third party software 
  • Email is sent from a Mobile device 
  • Email is sent from an Email Client other then Outlook that sends internal emails through SMTP rather than MAPI 
  • Email is relayed through multiple Mail Servers internally, which communicate through SMTP between them. 
  • The same Email Domain is spread through Mail Servers physically located on different cities/countries (communicating outside the LAN)

Workaround

The below can be implemented as a workaround: 
  1. Stop SMTP or Exchange Transport service
  2. In the MailEssentials Configuration, go to General Settings > Settings > Local Domains
  3. Remove the domain from the list and click Apply
  4. Go to the Whitelist, add the desired entries and then click Apply (in this case, *@domain)
  5. Go back to Local Domains, re-add the domain and then click Apply
  6. From the configuration, go to Anti-spam filters > Anti-Spoofing and enable it adding the IP address of SMTP server/s and then click Apply
  7. From the configuration go to "Filter Priority" and make sure that Antispoofing is above the whitelist
  8. Restart the service stopped in step 1
What the above does is, Anti-Spoofing will let pass through any internal email which has an authenticated connection with Exchange through SMTP. If the internal email makes it through Anti-Spoofing, the global whitelist will whitelist it so that it is not stopped by another filter. 

Note: enabling Anti-Spoofing is important for the risk of being impersonated by spammers since there will be email addresses from the local domains in the whitelist module.