- Mail Server Details
- Mail Issues Ticketing Form
- Email Settings
- How Email Works
- Advanced / Technical Details / Spam
- Outgoing Email Account Setup (SMTP Server)
- Attachment Problems?
- Changing your SMTP Port in Outlook Express
- Bounce Messages Explained
- 551 - User Not Local Errors
- Email Acceptable Use Policy
- Deleted Emails
- Spam FAQ
- Email Account Admin
Computers cannot unfortunately determine from an email whether it is spam, or an actual email.
So, to ensure that clients don't get inundated with too much spam, we have a system of filters in place to reject mails.
We currently receive around a million incoming emails delivery attempts daily. Of these approximately 90% are rejected in first round checks (spam listings), then others are filtered out with other rules 3-5%, and another few percent are rejected with content analysis. Final mail deliveries are in the 50,000 mails a day range.
This means that approximately 95% of incoming mail is rejected for failing to pass our rules.
What that means is that for every 1 email we receive that passes our checks, we also get sent about 95-98 spam messages (that we reject).
This is in line with most other providers in the industry unfortunately.
Our implementation of filtering is below: (these have been in place for a number of years, and work quite well as a balance between too much rejection, and too little filtering).
Our servers have the following pre-requisites for accepting mail from others (in order of precedence).
- 1.Sending Server has a valid Reverse DNS Entry
- 2.Sending Server conforms to mail RFC's
- 3.Sending Server is not listed in any of the following Antispam Service Lists zen.spamhaus.org cblplus.anti-spam.org.cn cdl.anti-spam.org.cn bl.spamcop.net dnsbl.njabl.org
- 4.Mail does not contain a virus, malware or similar content.
- 5.Mail is addressed to a valid sender.
- 6.Recipients mailbox is not full.
If any of these requirements is not met, the mail will be rejected, and an appropriate message sent back to the sending server.
If a server is listed, we reject all mails from that server, as they are most likely spam (and clients don't want spam). Some of those filters are mandated by our ISP (i.e. we're told by the government / regulating bodies in China that we must use them), others are personal choice based on years of experience.
If a given mail server / ip address is listed in one of these filter lists, this affects valid mails from those mail servers,as they're also rejected.
The good news is that generally those issues are cleared up quite quickly, as the users on that provider complain that they can't send emails to people, and their provider cleans up whatever issue caused them to be listed, and life goes back to normal.
In all cases though, listing is because of spam issues (i.e. their ip *is* sending spam out), not because we arbitrarily reject mail.
As no method is perfect, and people do have occasional issues (like where your sender is listed, so cannot send you mail till their provider resolves their spam listing issue),
we have also implemented user configurable rules for clients.
What that means is that you can decide if you want some, all or none of the blacklist rules in place to be in use, you can manage that yourselves..
The ruleset features are available at http://rules.computersolutions.cn
An overview of how to use them to whitelist senders is here -