I'm pretty sure it was because we use VERP_PERSONALIZED_DELIVERIES and the list has hundreds of digest members.

Right, I missed that in https://bugs.launchpad.net/mailman/+bug/558128/comments/5 when I wrote https://bugs.launchpad.net/mailman/+bug/558128/comments/6 -- You received this bug notification because you are a member of Mailman Coders, which is subscribed to GNU Mailman. https://bugs.launchpad.net/bugs/558128 Title: remove 552 exception for SMTP perm/temp To manage notifications about this bug go to: https://bugs.launchpad.net/mailman/+bug/558128/+subscriptions