Difference between revisions of "Scanning of email"

Revision as of 16:09, 13 June 2012

Emails sent to, from and within IMM are being scanned for viruses and unwanted attachments using MailScanner, spamassassin, CLAM antivirus/McAfee on the central DTU mailscanner.

The direct consequences for IMM users are:

• Senders from outside DTU are subject to greylistning, hence an email might be delayed up 4 hours.
• Mails which contain a virus recognized by either (or both) McAfee and ClamAV are being deleted immediately. Even if the virus is contained in a zip file.
• Mails with a high spamscore (given by spamassassin) are not being forwarded to the end user but send to a temporary storage where it will be available for a week.
  Mails with a medium spamscore will be forwarded to the end user but with the subject prefixed with [DTU-SPAMWARNING].
  Many viruses received by IMM can not be detected by ClamAV and McAfee because the viruses are "brand new", i.e. leaving no time for antivirus manufactures to produce pattern files to detect them. Because of this IMM stops many "risky" attachments. Files with extensions of .exe, .com, .dll, .vbs and many more are not permitted. An email which has any of those attachments will get the attachment(s) stripped off; and the email will be sent to the original destination as planned but with a message informing the recipient that the attachment has been stripped of and he/she should contact IMM ITSupport to receive it. The sender will not receive any notification. If the "illegal" attachment is placed in a zip file, the zip file will be stripped off. One way to bypass this is to rename an attachment from e.g. "program.exe" to "program.dtu".
  You may also rename the zip file to e.g. file.dtu, to avoid sscanning of the contents.
• IMM does not allow attachments greater than 40MB (since attachments have to be encoded with 7bit encoding this corresponds to a file size of about 15MB). However, many sites outside IMM only allow half the size.

Best practice hint concerning Outlook and Junk-Email filtering: while Outlooks junk filter does catch a number spam mails IMM experience shows that it does produce a number of false positives. make sure to check the "Junk E-mail" folder regularly.