Know the cause of the error "Sender Domain Not Found", and how to take action if you encounter this error.
Trend Micro Email Security (TMEMS)
To resolve this issue, you can add the email sender to the Approved Sender list. It can then bypass the sender domain check.
Hosted Email Security (HES)
The sender domain may not have a valid TXT DNS record, as well as a valid A record or MX record published on the public DNS Record. This is the reason why HES was not able to lookup the domain. One of the processes of HES for checking emails that pass through is to lookup the domain and make sure that it will be able to pull up a valid DNS record. However that is not the case for this particular domain.
To check whether or not a Sending Domain has a valid DNS record, do the following steps.
Check via NSLOOKUP:
- Open the Command Prompt and run it as an administrator.
- Type the command "nslookup <Sender domain>".
- Press ENTER.
- If the Sender domain does not have a valid DNS record, it will return the error "Non-existent domain".
Check via MxToolbox:
- Go to MxToolbox.
- Go to DNS Lookup tab.
- Type the sending domain under the field and click DNS Lookup.
- If the Sender domain does not have a valid DNS record, you will receive an error as shown below:
A non-registered domain is not allowed even if it will be added on the Allowed Senders list. This is for security purposes and HES is RFC compliant which is the Anti-Spam standards that are defined under RFC 7505.
It is strongly recommended to have the domain sender create an MX/A record to have their domain published.