Reducing spam received

[ngophotographer]

Hi folks,

I use Mail Station and Mail Server on my Synology NAS, and Synology Support have directed me here, saying that the "Mail Station application is an implementation of Roundcube and as such is not something that we have developed, only adapted to work on the NAS device". I hope you'll be able to help me. 

I get an awful lot of spam, about a third of which gets marked *****SPAM***** and goes to my Roundcube Junk folder, while the other two-thirds goes to my inbox. Am I right in thinking that the attached image shows the best way to stop particular domains that are responsible for a lot of the spam from getting their messages through to me? If so, what I'm confused about is this option:

'From:' address contains this domain: Mail domain (e.g. 'mail.example.com')

I am used to setting up filters for *@example.com in Gmail to catch every single address that ends '@example.com'. For Mail Station / Roundcube, do I need to write 'mail.example.com' or 'mail.flashlights.com' or 'mail.free-trump-coins.com' instead of '*@example.com' or '*@flashlights.com' or '*@free-trump-coins.com'? Or have I misunderstood?

Also, would selecting 'Reject it' result in incoming mail being sent back to the sender with a failure report?

Thanks and warm wishes to you!

[SKaero]

Unfortunately you most likely wont get help here since Roundcube is only a webmail client and therefore doesn't perform any spam filtering. The screenshot you posted isn't from Roundcube so I would think that is a Synology interface although I could be wrong.

[rm13]

That's the Synology interface and not a part of Roundcube.

There are Synology user forums that would be of better assistance in dealing with the spam filter, SMTP, and IMAP functions of the email server.

That does look like the place to create filtering rules. And those Synology forums would be the place for specifics. The downside to filtering on a domain is that the spammer may be spoofing that domain and you risk cutting off legitimate email. Creating a user level filter would be less risky than a server level rule. If there is also Spam Assassin installed (not a part of Roundcube either) then you may be able to change the scoring level to improve results. Consider filtering on keywords or content rather than a domain.

Rejecting spam would typically bounce it back to the sender, but if not properly handled it creates backscatter by bouncing to spoofed addresses and possibly assisting in spam delivery. If in doubt just drop or delete the spam.

[ngophotographer]

Thanks, both of you! Sorry for inadvertently posting a non-Roundcube issue to this forum, and thanks for your understanding and help. I returned the enquiry to Synology, who just replied with this:

Apologies for the confusion, on looking at your original screenshot once more, I have realised my mistake that this is of the Mail Server application and not from Roundcube as I originally thought it was.

With regards to the blacklist entries themselves, if you are aware of the mail domain address (eg. mail.synology.com) you can add it in this format, however as an alternative using synology.com as an example should also work in this instance.

To create black and white list rules:

Click the Black and White List button.
Click Create.
Specify the criteria for the rule, for example:
If you specify the IP address as "192", the messages from "192.*.*.*" will be targeted.
If you specify the email address as "admin@", the messages from "admin@domain" will be targeted.
Choose what to do with messages that fit the criteria:
Reject it: The message will not be sent from or received by Mail Server.
Accept it: The message will be accepted whether or not it was blocked by the DNSBL list.
Discard it: The message will be discarded. Mail Server will not inform the sender.
Click Finish to save settings.
Source: https://www.synology.com/en-uk/knowledgebase/DSM/help/MailServer/mailserver_spam