Will outgoing SMTP spam filter work for forwarded alias emails?
Question asked by JohnC - 11/20/2021 at 9:02 AM
My Smartermail is installed on a godaddy vps. And all outgoing email needs to go through godaddy's SMTP relay servers.

I have an alias setup that simply forwards any mail to it out to a gmail address.

So, if spam comes into that alias, it will immediately be sent to the gmail address.

And what I am thinking is that when gmail starts seeing an excess of spam, it may report my smartermail server as the "source" of that spam because I'm thinking that when smartermail forwards the spam messages via the alias, it is making a separate SMTP connection to gmail, so google thinks the email is coming from my server instead of the real (original) sender of that spam.

I see that I can setup "outgoing SMTP spam filtering".

So, If I enable outgoing SMTP spam filtering, will that filter the email being forwarded (sent out) via the alias I setup (which forwards the emails to a gmail account)?

My hope is to setup the system so that any incoming email to the alias is tested for spam, and if found, it will NOT forward it to the external gmail address.

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Douglas Foster Replied
Concentrate on INBOUND blocking.   If it does not get delivered to your mailbox, it does not get forwarded.   If you have more than one mailbox, inbound blocking helps all mailboxes.   

Outbound blocking should be configured to prevent an infected machine from spamming.   If you manage to avoid infected machines, you don't have to worry about outbound blocking.

But you have also identified the reason why auto-forwarding is, in my mind at least, a terrible idea.   It hinders the downstream server from making correct filtering decisions because both wanted and unwanted sources are hidden behind your forwarding server.  We can assume that the filtering rules in a downstream server will be different from your filtering rules.  If your server is too strict, you lose messages.   If your server is too lax, you get blacklisted as a spam source (and also lose messages.)   So if you insist on auto-forwarding, you should be certain that your filtering is really good before you enable that feature.

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