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Bielefeld IT Service Center

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© Bielefeld University | BITS

Mail Policy

The current status of the policy (set of rules for handling e-mails) of the mail server of Bielefeld University is described here.

  • The incoming mail gateways are provided and operated by DFN-Verein (DFN MailSupport).
  • All other components are implemented by Microsoft Exchange.
  • When establishing new mail servers/domains within the university/university of applied sciences, BITS must be contacted to establish the necessary MX records in the DNS and to set up mail routing.
  • The validity of mail addresses is verified using the "call-forward" procedure. When the mail is delivered to the gateway, the mail address is checked via SMTP dialog on the destination server. If it is known, the mail is accepted and delivered. Otherwise, acceptance is rejected (500 return code). In case of failure, the delivering server receives a (temporary) delivery error (400 or 500 return code).
  • Virus handling: The gateways scan the mails for known viruses when they are delivered. Mails that contain viruses are rejected (500 return code). Otherwise, further processing takes place.
  • Handling of SPAM: The gateways evaluate mails on delivery and distinguish between 3 cases (mail policy message).
    • Rejection based on the sender IP:
      The computer/server sending the e-mail is on an IP block list because SPAM or e-mails containing malware have been sent from this IP. If you have been wrongly placed on this list, first contact your local e-mail support (postmaster@ihre-domaene.xy). This person can then clarify the issue with BITS support.
      In case of a general problem, the deletion of the IP address can be requested.
    • Rejection due to high SPAM probability:
      The delivered e-mail contains numerous characteristics of a SPAM e-mail (e.g. many links or embedded images).
    • Rejection because the e-mail contains a virus:
      The delivered e-mail has been checked and the virus scanner has found a known virus. Please have your computer checked for possible malware. If you are absolutely sure that it is not infected by a virus and the content of the e-mail was falsely detected as a virus, please contact BITS support.

    • Rejection due to Microsoft Office formats in attachments containing macros:
      The following (old 97-2003) formats are processed:
      doc dot pot ppa pps ppt rtf xl xla xls xlt xslb
      docm dotm ppam potm ppst ppsm pptm sldm xlm xlam xlsb xlsm xltm xps
      The following (new XML-based) formats cannot contain macros by definition and are therefore not checked:
      docx dotx potx ppsx pptx sldx xlsx xltx
      If possible, please do not use old Office formats and disable macros in general. If it is unavoidable, please use other exchange options, e.g. Sciebo.

  • Operators of their own mail services can receive all SPAM mails on request. Please contact BITS support for more information.
  • Limitation of IP connections per time unit for computers on the Internet. If a threshold is exceeded: temporary delivery error (400 return code).
  • Limitation of the number of e-mails per time unit and sending e-mail clients/servers. Different rates are configured for the intranet and the Internet. - Exceeding: Temporary delivery error (400 return code).
  • RBL (Realtime Blackhole List) lists:
    • RBL lists are used for spam evaluation.
    • A very reliable list of IP addresses maintained by DFN mail support is used to reject mails from these senders.
  • Blocking of known sender/destination addresses statically used by viruses, such as admin@duma.gov.ru by the W32/Dumaru-A virus, if this seems reasonable.
  • To prevent disk space quota problems when deleting mails and thus moving them to the Deleted Items folder (Trash), they are automatically deleted there after 40 days. (active from 01.12.2022)
  • Spam rating: the SPAM rating (scoring) is done according to the default settings of the DFN-Mailsupport and adapted to the current recommendations. More detailed information can be found on the DFN MailSupport website.

Restrictions on e-mail traffic

BITS ultimately cannot prevent a university identifier with a person's associated password from falling into unauthorized hands. These 'hacked' accounts have been abused in the past for mass distribution of unsolicited emails (SPAM and phishing).

This threatens the rejection of emails from the university by so-called blacklisting of our email domain with other email servers. In order to curb this problem, there are the following limits on sending:

Outlook, Webmail and ActiveSync
Max. Number of messages per minute: 10
Max. Number of receiving addresses (To, CC, BCC) per email: 200
Max. Number of receiving addresses (To, CC, BCC) per mailbox per day: 1000 (regardless of the number of messages)

Example: For example, if you address 50 recipients* in an email, you can send a maximum of 20 of them per day.

SMTP (e.g. Thunderbird)
Max. Number of messages per minute: 5
Max. Number of recipient addresses (To, CC, BCC) per e-mail: 200
Max. Number of receiving addresses (To, CC, BCC) per mailbox per day: 1000

Example: For example, if you address 200 recipients* in an email, you can send a maximum of 5 of them per day.

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