We sent out a mailing the other night to roughly 200 subscribers and they received multiple copies, some people received it 6 times. I've checked the logs although nothing much was logged in the CMS Desk log I found the following in SQL and Server logs at around the time we sent it.

In the SQL log - 'Error 7886. Severity: 20, State: 1'
followed by
'A read operation on a large object failed while sending data to the client. A common cause for this is if the application is running in READ UNCOMMITTED isolation level. This connection will be terminated.'

In the server log - 'Event ID 1334 - Message: [DataConnection.ExecuteQuery]: Query: SELECT * FROM Newsletter_Emails WHERE [EmailID] = @ID: caused exception: A transport-level error has occurred when receiving results from the server. (provider: TCP Provider, error: 0 - The specified network name is no longer available.)'
followed by
'Event ID 5000 - EventType clr20r3, P1 w3wp.exe, P2 6.0.3790.3959, P3 45d6968e, P4 cms.dataprovidersql, P5 3.0.2950.31898, P6 479f57a5, P7 25, P8 196, P9 system.exception, P10 NIL.'

The CMS application had to be restarted after this as it wasn't behaving correctly, it seemed to have lost access to the resources file as all the labels for tabs, forms, error messages etc were not displaying correctly.

Any idea what may have caused this to happen, have you experienced anything like this before with the newsletter module? We are on version 3.0.