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We recently had an issue with someone forwarding their email from their yahoo.com address to their on site mailbox. Unfortunately someone on the mailing list received a meeting request and accepted it which then responded back to 4 lists on the original request.  One of the four lists had over 25k subscribers.  There were 4 lists all were set to moderated except for the large 25k + list which is set to only allow subscribers to send.

After the person who accepted the message received many threats they decided to cancel the meeting request several times.  Which then compounded the problem.

Summary: over 4 million messages flooded the sympa server for delivery and basically worked like a denial of service for sympa for a couple of hours.

 

We now know to lockdown large subscriber list to some type of moderation.

We have run several tests and found that yahoo.com does not process accepting and cancelation requests the same as google.com or Hotmail.com. For each action yahoo sends 3 messages for each action where the others send only one.

 

Does anyone have any experience with this or ideas on how to monitor and resolve this bottleneck quickly.

Your assistance is much appreciated.