Can't Send Emails to Domains hosted in "Barracuda Email Essentials"

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2 posts Page 1 of 1
by brce » Tue Mar 03, 2020 3:14 pm
Sometime early last week we started getting error: "421 4.4.0 Remote server response was not RFC conformant" on any emails going to a few domains. After looking into it more I ran MX Lookups on the domains with errors, they are all hosted by Barracuda and I can't get help from them because I am not a client.
The only thing I can think of is our reverse DNS does not match our MX record. Our MX record points to our IP address, but a revers DNS points to our
When I go into our host records in member tools, I can't find how to change the PRT or reverse DNS to match our MX record.
by joemuller » Thu Mar 05, 2020 4:17 pm
If this is for, it looks like you should be good now - I performed a quick lookup on your MX server (which looks to also share the same IP for outbound mail) - the reverse DNS gives a matching result of ''.

The report over at MX Toolbox shows no major errors that would be preventing mail from being accepted. If possible, could you forward the full headers from a bounced Barracuda email (from your domain) over to

-- Joe M
Sonic System Operations
I'm a proud employee of! :-)
2 posts Page 1 of 1

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