Current scenario:

We are hosting Lotus Domino Mail Server in our office with public domain. Live ip is configured on main gateway router. When any email from the internet arrives , it comes to our gateway router public ip, & router rules forward port 25 requests to domino server.

& when lotus user sends email, it delivers to domino server, and since the domino server have default gateway pointing to the gateway router, it simply sends email directly to the recipient. this is quite simple till now.

Now we have acquired Barracuda Antispam hardware device (model 300a) & as per the local barracuda vendor they are asking us that we must have SMTP relay server at our end in order to route user outbound emails from barracdua to the internet.

so If we remove barracuda from the picture, we dont need the smtp relay, and if we put barracuda why we need SMTP relay ? to send outgoing email, I can bypass barracdua simply right? because domino is using my gateway router as default gateway?

we dont want to relay emails to ISP SMTP relay because there public IP sometimes gets blacklisted this is why we want to use our own public IP.

So what should I do in this regard?

1 Answer 1


You are correct; Barracuda Spam & Virus Firewall doesn't require additional outgoing SMTP relay.

It's possible that your vendor simply doesn't know at least one the following:

  • the Barracuda Spam & Virus Firewall can work without a smart host
  • your Internet connection has port 25 open, allowing you to host own SMTP servers
  • you are planning to use the appliance merely for incoming mail.

Although it might be true, we don't necessarily need to claim them for being unskilled, because these could simply be assumptions that would be correct for most of their customers. Asking for an outgoing relay might be their standard procedure assuming you use this functionality and need to relay all message through you ISP. This also suggests that they are doing some pre-configuration instead of just delivering the product, which you could also configure by yourself.

See Barracuda Spam & Virus Firewall Administrator’s Guide. Relays are explained on (V5.1) p. 35:

Configure Scanning of Outgoing Mail

To scan outgoing mail with the Barracuda Spam & Virus Firewall, you must configure outbound operation on the BASIC > Outbound page. There you’ll specify your trusted outbound mail server IP address or domain name (either your mail server or another trusted relay), identify a Smart host if you have one, and, optionally, an authentication type. The Barracuda Spam & Virus Firewall supports SMTP/SASL authentication and LDAP.


  • trusted relay = your internal or external SMTP server, allowed to send outgoing mail i.e. allowed to send mail also to every domain that the device isn't configured to recognize:

    On the BASIC > Outbound page, you can configure the IP address and/or domain name of one or more outbound servers that can relay outbound email through the Barracuda Spam & Virus Firewall to the Internet. (Securing the Outbound Relay of Email, p. 49)

    Your Barracuda Spam & Virus Firewall will only accept emails addressed to domains that it has been configured to recognize. (Creating and Managing Domains, p. 92)

  • smart host = the outgoing relay, e.g. ISP's SMTP server; "if you have one" tells it is optional.

  • from your detailed answer, I assume that in order to scan inbound/outbound emails via barracuda, I dont need any extra smtp relay. my gateway router will forward incoming 25 port from the internet to barracdua, which will then scan and forward to DOMINO Server, and then when my LAN client will send email, DOMINO will handover mail to Barracuda IP (via using domino Relay host for messages leaving the local internet domain" , and Barracdua will use the default gateway (gateway router ip) to deliver the email . Am I Right ? (So No Relay Actually will be used here?) Apr 27, 2018 at 5:09
  • 1
    If Domino sends outgoing mail to Barracuda, you'd be using it for outgoing mail, too. If not, Domino sends the mail directly to the receivers MX. (Both incoming/outgoing goes via the router, but it's not SMTP aware; different layer, different story.) Apr 27, 2018 at 5:19

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