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FAQ: Why is my mail not being sent? (for mail server administrators)

Why do we block your mail server?

About 90% of the incoming connections come from servers that send SPAM. Because of this we are forced to impose different restrictions on mail servers (outside the UGent domain) that wish to send us e-mail.

These restrictions mean, among other things, that your mail server

• can make a limited number of connections
• can send a limited number of messages
• can open a limited number of concurrent connections
• must adhere to the SMTP protocol
• should not be on a blacklist

moreover

• the sender address must contain a fully qualified domain
• the sender and helo domain must exist

Error message(s):

451 4.3.2 Temporary failure greylisted

Cause:
Greylisting is a method to prevent spam. See http://en.wikipedia.org/wiki/Greylisting

How can you do something about it?

Our mail servers will give you an error message that contains enough information to solve the problem yourself. E.g. if you are on a blacklist, you will see on which blacklist this is, and you will get a url with additional information.

When your mail server is delayed (throttling), we recommend you to first check why you are bumping into our limits. If you cant find the cause, please contact the UGent Postmaster.

You must provide the following information:

• the error message
• the IP address
• the time of sending

HThe simplest is that you copy several lines from your mail server log files and email to us.