Email Policy

Our mail servers implement several techniques to reduce the number of delivered unsolicited email messages (UCE/UBE – commonly known as spam) to our users.

Notification

In case of rejection or any other error our servers ALWAYS provide an error message in the SMTP dialog which clearly indicates the source of the problem. A properly set-up email system should return the message to sender with our error message included.

If you don’t understand the provided error message or the descriptions on this page, ask the administrator of your mail server or your internet service provider.

You can ask us for help or advice by filling out our contact form, sending an email or calling us us by phone:
Web Contact Form: http://www.k18.ch/about/contact/
Email: support@k18.ch
Phone:+41 43 243 93 44
Please use our contact form if your emails fail to be delivered.

Whitelisting

If your emails get rejected and your service provider is unable to comply with the rules below, please contact us, so we can add your mail-server to our whitelist.

k18.ch Email Policies

This policy may change at any time without prior or further notice.

Incoming network connections to our mail servers must fulfill the following rules or the message will not be accepted for delivery:

Reverse DNS records

The connecting IP address must have a valid reverse DNS record.
Example SMTP error message:

550 Sorry, your IP needs Reverse-DNS to connect here. See http://www.k18.ch/policies/spam/

Valid Return MX

The domain of the senders email address should have a valid MX record in DNS.
SMTP error message:

554 refused mailfrom because return MX does not exist

Valid recipient

The recipient address should match a existing account name on our servers.
SMTP error message:

554 Sorry, no mailbox here by that name. (#5.1.1)

Real-Time Blackhole Lists and DNS Blacklists (RBL/DNSBL)

The connecting IP address should not be listed in one of the following real-time lists:

Example SMTP error message:

553 sorry, your mailserver [83.69.224.124] is rejected by Spamhaus ZEN - see http://www.spamhaus.org/zen/

Number of Recipients

The number of recipients for an email message should not exceed 200 addresses.

Mail Message Size

The size of any incoming or outgoing emails should not exceed 20 Megabytes.

Mails with File Attachments

The following 45 file types are considered as potentially harmful. Messages containing any of these file types as attachments will be rejected by the server immediately.

ad – Microsoft Access Project Extension
ade – Microsoft Access Project Extension
adp – Microsoft Access Project
asp – Active Server Page
bas – Microsoft Visual Basic Class Module
bat – Batch File
chm – Compiled HTML Help File
cmd – Microsoft Windows NT Command Script
com – Microsoft MS-DOS Program
cpl – Control Panel Extension
crt – Security Certificate
exe – Program
hlp – Help File
hta – HTML Program
inf – Setup Information
ins – Internet Naming Service
isp – Internet Communication Settings
js – JScript File
jse – Jscript Encoded Script File
lnk – Shortcut
mdb – Microsoft Access Program
mde – Microsoft Access MDE Database
msc – Microsoft Common Console Document
msi – Microsoft Windows Installer Package
msp – Microsoft Windows Installer Patch
mst – Microsoft Visual Test Source Files
pcd – Photo CD image, Microsoft Visual Compiled Script
pif – Shortcut to MS-DOS program
reg – Registration Entries
scr – Screen Saver
sct – Windows Script Component
shb – Shell Scrap Object
shs – Shell Scrap Object
url – Internet Shortcut
vb – VBScript File
vbe – VBScript Encoded Script File
vbs – VBScript File
vsd – Microsoft Visio File Type
vss – Microsoft Visio File Type
vst – Microsoft Visio File Type
vsw – Microsoft Visio File Type
wmf – Windows Metafile images
wsc – Windows Script Component
wsf – Windows Script File
wsh – Windows Script Host Settings File

Example SMTP error message:

554 Your email was rejected because it contains a bad attachment: trojan.exe

Virus Infected Mail

All incoming and outgoing emails are scanned for viruses. If a virus is detected, the message is rejected immediately.
Example SMTP error message:

554 Your email was rejected because it contains the Worm.Bagle.AU virus

Spam Filters

All incoming emails are scanned by SpamAssassin with additional plugins and a customized rule-set. Messages with 5 or more hit points will be delivered to the users junk-mail folder and marked as spam. Messages with 10 or more hit points will be rejected by the server immediately.
Example SMTP error message:

554 Your email is considered spam (28.80 spam-hits)

Sender Policy Framework – SPF

We check the sending server for SPF compliance. As this test is performed by SpamAssassin, mails will be rejected as spam (+10 points). Currently no custom error message is returned.

Dynamic IP Address

The connecting IP address should not be a dynamic address (like home computers, ADSL, dial-up lines, cable-modems and others). Use the mail server of your internet service provider or organization. As this test is performed by a SpamAssassin plugin, mails will be rejected as spam (+10 points). Currently no custom error message is returned.

No Open Relay or Proxy

The communicating server must not be an open proxy or open relay and must be protected against unauthorized access.

RFC Compliance

E-Mails must comply to the standards described in RFC 2822. A complete and plausible HELO/EHLO as described in RFC 2821 must be sent.

Valid Sender Address

The address of the sender must be a correctly formatted internet email address (with an @, a . in domain part and not too long or too short top-level-domain (TLD).

We do not Relay

We do not accept messages for domains which are not hosted on our servers.
Example SMTP error message:

553 sorry, relaying denied from your location [83.69.224.124] (#5.7.1)

Bounce Message with multiple recipients

We do not accept bounce messages with more than one recipient.
Example SMTP error message:

550 sorry, I don't accept bounce messages with more than one recipient. Go read RFC2821. (#5.7.1)

Statistics

The graph below shows handling of incoming mail-server connections on a typical day in November 2007.
SMTP-MTA Graph

k18.ch