Long time processing for delivery send - v8

Hi,

I've just started working with ACC v8 and I'm looking for a way to get a better performance on email deployment.

I have a workflow that targets around 1 milion records, the query is based on default recipient table, it excludes from the target email address from particular providers and checks if tracking logs exist. Running it without delivery attached at the end goes smoothly - after 2 minutes I can see results under 'display the target' option.

The situation changes dramatically when I try to use the audience to send the delivery. Executing the query still takes around 2 minutes but preparing a delivery - around 3 hours and sometimes it fails with error: 

'ODB-240003 ODBC: Unable to retrieve error message.'

Adding a split activity and trying to send the message in smaller batches (250k) has the same result.

I'd appreciate any input of this.

Thanks,

Dominik