To manage the content that is forwarded by the mail gateway, you can configure blacklists and grey listing. You can also configure the mail gateway to strip specific types of content from mail.
Configure Content Stripping
You can configure the mail gateway to strip the following content:
- Attachments – Strip specific attachment file types before forwarding mail to recipients. You can also exclude specific senders and recipients from having attachments stripped from their mail.
HTML Tags – To protect your network from HTML email with annoying or potentially dangerous content, such as hyperlinks leading to fake websites and images with objectionable content, configure the mail gateway to remove HTML tags. As a result, links lose their function and images can no longer be loaded. Users are prevented from clicking on links unintentionally or thoughtlessly.
- Received Lines – Every SMTP server or relay registers itself within the mail header. These received lines may contain internal and confidential information about mail infrastructures. When the received lines are stripped, the number of "received" lines in the header stays the same but the content is replaced by dummy entries and thus no longer contains security critical information.
- Barracuda Networks ID – Remove the Barracuda Networks ID from the mail header of dispatched email. This can help conceal the identify of the mail gateway and decrease software traceability.
To configure content stripping, complete the following steps:
- Go to CONFIGURATION > Configuration Tree > Box > Virtual Servers > your virtual server > Assigned Services > Mail-Gateway > Mail Gateway Settings.
- In the left menu, select Content Adaptations.
- Click Lock.
Specify the content to be stripped. Follow the steps in the following table for the content that you want to be stripped from mail:
Task Steps To strip attachments: - In the Attachment Stripping section, select yes from the Enable Attachment Stripping list.
Next to Advanced Attachment Options, click Set or Edit.
Edit the attachment stripping settings. For more information on these settings, expand the following Settings Overview section:
Settings Overview- Click OK.
To strip HTML tags: - In the HTML Tag Removal section, select yes from the Remove HTML Tags list.
- To remove link tags, select yes from the Remove HTML Link Tag list. Links lose their function, but the string of the link itself remains unchanged. The linked destination can be viewed by copying the link from the email and pasting it into the address field of the browser.
- To remove image source tags, select yes from the Remove HTML Img Src Tag list. Image source tags are altered so that they lose their function. Linked images will no longer be loaded from the servers they are placed on. Keep in mind that this function destroys the design of incoming and outgoing HTML email (such as newsletters).
To strip received lines: - In the Misc section, select yes from the Strip Received Lines list.
- In the Strip Received Lines Text field, enter the text that replaces the original text that is stripped from the email header.
To remove the Barracuda Networks ID: In the Misc section, select yes from the Remove Barracuda Networks ID list. - Click Send Changes and Activate.
Configure Grey Listing
Grey listing helps reduce SPAM by initially rejecting a message with an unknown sender-recipient pair. A rejection notice is sent to the mail server and the sender-recipient pair are placed on the grey list. The mail server is also told to try sending the mail again. A mail transfer agent (MTA) that has been correctly configured will attempt to resend the mail. The second delivery attempt is accepted and the email is delivered. Typically, SPAM is sent by non-RFC conforming servers that ignore error reports and do not try resending mail.
With grey listing, consider the following:
- Depending on the configuration of the sending MTAs, the email sender might be issued a report about the initial delivery failure.
- There is a slight delay in mail delivery because emails are initially rejected.
- Wanted emails may not be delivered if MTAs for the sender are not correctly configured. In this case, you can add the sender to the whitelist in the grey listing configuration.
To configure grey listing, complete the following steps:
- Go to CONFIGURATION > Configuration Tree > Box > Virtual Servers > your virtual server > Assigned Services > Mail-Gateway > Mail Gateway Settings.
- In the left menu, select Content Adaptations.
- Click Lock.
- In the Grey Listing section, select yes from the Enable Grey Listing list.
Next to Advanced Grey Listing Options, click Set or Edit.
Edit the grey listing settings. For more information on these settings, expand the following Settings Overview section:
Settings overview- Click OK.
- Click Send Changes and Activate.
Configure Blacklists
Mail Blacklists prevent incoming mails from being forwarded. To block certain hosts, subjects, sender, or recipients, add them to the blacklist.
- Go to CONFIGURATION > Configuration Tree > Box > Virtual Servers > your virtual server > Assigned Services > Mail-Gateway > Mail Gateway Settings.
- In the left menu, select Content Adaptations.
- Click Lock.
- In the Blacklists section, select yes from the Enable Blacklist list.
Next to Blacklists, click Set or Edit.
Add the hosts, subjects, sender, or recipients to the blacklists. For more information on the blacklists, expand the following Blacklists Overview section:
Blacklists overview- Click OK.
- Click Send Changes and Activate.
Continue with How to Configure Mail Gateway Service Limits.