ListManager is unable to send mailings if it gets incorrect information when doing DNS lookups for external or specific domains.
The first thing to determine is whether ListManager is actually doing the DNS lookup using its own DNS resolver, or if you have decided to use your own DNS server:
- Navigate to "Utilities : Administration : Server : Server Settings : Network Settings" and select the DNS tab.
- If there is a server IP address listed, and "Use only for fallback" is set to "no", then you are not using ListMangager for your DNS lookups and will need to work with your IT department to troubleshoot the issue.
- Otherwise, the following suggestions can help you troubleshoot the problem.
Use MXToolbox to see what IP address should be used to send mail to this domain.
2. Compare with ListManager's built-in DNS resolver
Go to "Utilities : Administration : Server : DNS Diagnostic Tool", enter the domain you would like to check, and click "submit".
Compare your results with the output received from MX toolbox to see if there is a discrepancy.
3. Clear the DNS cache for the domain (or all domains)
If there is a discrepancy between ListManager and MXToolbox, and you are also having problems sending to this mailing, you may need to clear the DNS cache for that domain.
If ListManager has a bad DNS entry cached for a domain it will report a mailstream block on that domain and the SMTP log will show a Connection Refused error if there is no mail server hosted at the old IP. If there is a mail server at the old IP there will be a bounce.
If the cache is not flushed the entry will not expire until the TTL (Time To Live) for the entry is reached.
ListManager's DNS cache can be flushed of all domains by restarting the ListManager server.
You can clear the cache for a specific domain by using these steps:
- Navigate to:
- Click on "Tcl Terminal"
- Click on the check box "Use TclPort"
- In the top window, type in the command:
clear_dns_cache domain(name of domain).
- Click the "Execute" button (no need to restart the server nor services if only clearing the cache for a specific domain).
4. DNS Bypass for the domain
Flushing the DNS cache may resolve the issue temporarily, specifically the length of the TTL for the domain entry. After the TTL expires, it's possible there will be issues resolving to the domain automatically.
To avoid having to flush the DNS cache on a regular basis, it may be desirable to manually set the routing to a specific domain. This is done in ListManager by way of a DNS bypass entry.
Use MXToolbox to identify the IP addresses for the MX records used by the domain.
To create a DNS bypass entry:
- Navigate to "Utilities : Administration : Server : Server Settings : DNS Bypass"
- Click the "Create New DNS Bypass" button
- For the "Domain" field, enter the domain for this DNS bypass entry, e.g., example.com
- For the "Hostname" field, enter the hostname for the MX (must be unique if creating multiple entries for the same domain), e.g., mx1.example.com
- For the "Type" field, select MX
- For the "Address" field, enter the TCP/IP address for the NS or MX domain.
- Click "Save".