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Greylisting Help

Greylisting uses to filter spam and viruses.

You came here probably after seeing an email of yours being rejected with a message like this:

Greylisted for 300 seconds.

The mail server generating this error message is using a system called Greylisting to filter spam and viruses. It relies on mail servers behaving according to the standards and usually doesn't require any action by the user. Your mails should only possibly be delayed.

If you see this error message while sending a mail from within KTH, it probably means that you did not configure your email client to use exchange or smtp.kth.se

Instructions for configuration can be found at

If you are the postmaster or the system adminsitrator of a site that cannot deliver emails to KTH the most likely reasons are:

  • The email is generated by a web application and not a proper email server, please configure your application to use an outgouing emailserver.
  • You are using an old Microsoft Exchange server that cannot handle greylisting properly, please increase the Glitch Relay setting in the registry to more than 300 seconds.
  • A broken/misconfigured cloud service is used, ask the provider to fix it.
  • You have configured your service to use IPv6 but you or your ISP did not get i quite rigth yet, please disable IPv6 until you know that the routing is working correctly.

See this page for a description about how Greylisting works. en.wikipedia.org/wiki/Greylisting (external page)
If you for some reason cannot fix this problem contact itsupport@kth.se and ask to get your email address whitelisted.

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Page responsible:it-support@kth.se
Belongs to: KTH Intranet
Last changed: Nov 18, 2020