Applies to all Barracuda Email Security Gateways, all firmware versions.
There is no way to stop a spammer from using any one email address for the spam they send out. There are however things that you can do to help prevent this from becoming a huge problem. These would be setting up SPF, DKIM and/or DMARC services for your domain. This will let people who receive email from your domain block sending IP addresses or senders who are not authorized to send mail for your domain. Although these can be used in conjunction with the SPF settings on the appliance to provide sender spoof protection, there are additional settings on the device, designed to address this specifically.
Here's the scenario: You manage "domain.com" and spammers are pretending to be legitimate senders from your domain, like firstname.lastname@example.org or email@example.com. The Barracuda Email Security Gateway can block this sort of domain spoofing, but it is not always safe to do so.
The Barracuda Email Security Gateway's sender spoof protection blocks all emails that claim to be from any domain configured on the Barracuda. This is fine for internal users that do not go through the Barracuda when emailing each other, but when these users send email to users at other domains through the same Barracuda, the Barracuda will see that these emails are from a domain that it hosts and block them. Also, it is not recommended to enable the Sender Spoof Protection option if your legitimate users are sometimes on the road and send company e-mail from external mail servers (unless those mail server IPs are whitelisted). These will be blocked for the same reason.
Firmware version 3.5.x and earlier
Log into your Barracuda Email Security Gateway’s web interface and go to the Advanced > Email Protocol page. Find the setting for Sender Spoof Protection and set it to Yes. On Barracuda Email Security Gateway models 400 and higher, this is also a per-domain setting that can be configured on the Domains > Edit Domain page for each configured recipient domain.
Firmware version 4.0.x and later
Log into your Barracuda Email Security Gateway’s web interface and go to the Advanced > Email Protocol page. Find the setting for Sender Spoof Protection and set it to Yes. On Barracuda Email Security Gateway models 400 and higher, this is also a per-domain setting that can be configured on the Domains > Manage Domain (select your domain) > Advanced > Email Protocol. Next, set Reject messages from my domain to Yes.
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