6/1/2011 11:38:32 PM
RE:[5.5.0] Newsletters sent to each subscriber twice?
You're posting to a sub-forum "Version 5.x", while your client has 3.1 version, that's why you also don't have "Email queue" in Administration section, because it has been added in 4.0 version.
There were some issues reported with newsletters earlier, but often related to changes and repeated sending, as Helena suggests above.
As for the event log - have you checked the Event log in Site manager -> Administration, with site selection "(global)" ?
We would anyway recommend upgrading to the current version.