Protection against SPAM

Stricter user guidelines for sending e-mails

To minimize the effects of spam sent via the webmailer or one of the SMTP servers (“”, “”) via a hacked ID, the user guidelines for the webmail and SMTP service were tightened.

Using the following conditions, we try to determine misuse of our services.

Should one of those rules be broken, the affected account will be locked to protect the other users of the mail system!

These restrictions should not impede the usage of the e-mail services. Should you need to push the boundaries of our user guidelines because of certain mail procedures and therefore need an exception for said guidelines, please contact the hotline or e-point, so your needs can be met in a timely manner.

Rules for webmail

  • Within one day you can send mails from your account to up to 900 recipients.
  • You can only send one mail every 10 seconds. This prevents automated, script controlled sending of mails via a compromised ID.

Rules for the mailout-server

  • A user authenticates him- or herself more than 150 times within one day on the SMTP server to send an e-mail.
  • An e-mail software (identifies by the used IP address) sends mails to more than 900 recipients within one day.
  • An e-mail address is used to send mails to more than 900 recipients.

Maximum number of recipients

In addition, there is a maximum number of recipients for one single mail: You can send one mail to a maximum number of 99 recipients (To:, CC: and BCC:).


A violation of these rules leads to an automatic block of your ID for the e-mail services. The user will receive a notification about the blocked e-mail and the reasons behind it.


The user receives the following notification:

„Ein Fehler ist aufgetreten! SMTP Fehler: [451] 4.3.0 <IHRE-E-MAIL-ADRESSE> ... not allowed because of spam distribution!“


„An error occured! SMTP error: [451] 4.3.0 <YOUR MAIL ADDRESS>… not allowed because of spam distribution!”

You can still login to the webmail interface and read your mails, but sending mails is no longer possible. It is possible however, that even the login fails, because your access to the webmailer might be blocked. You will get the error notification “Verbindung zum Speicherserver fehlgeschlagen“ (“Connection to IMAP server failed.“)


The e-mail program cannot send the mail. You receive one of the following error messages:

<Login-ID/Unikennung>… not allowed because of spam distribution!”


<IP address>… not allowed because of spam distribution!”

Other university services like WI-FI access, LSF and the Selfcare-Portal etc. are not affectes by this and can still be used.

Should we have the justified suspicion, that your ID was hacked, then the other services will be blocked as well.

Help in case of a blocked ID

To reactivate your ID, a ZIM employee needs to lift the block. Please contact the hotline for this. The reactivation will be performed as soon as possible.

Restrictions for mail traffic

You can find information on maximum e-mail sizes, attachments, quota etc. in our mail policy. It is described there, how detected viruses and executable attachments are dealt with.

Why is protection against SPAM necessary?

You can find information on the consequences of SPAM for the university here (german).