Before you send any messages, always send one or two to an email address you have access to. Check the recieved messages to see if they are exactly as you want them to be recieved, there is no undo!
In your messages you should always provide a way for the recipient to unsubscribe from your lists, in many countries this is actually a legal requirement.
When you press the Deliver... button, you will be asked to confirm, and if you've selected some recipients in the list, you will be asked if you want to send to the whole list, or just the selected ones.
Once you have confirmed you want to send, the messages will start being sent, this may take some time depending on your quota set by Amazon, and of course, the size of your mailing list.
When your email is sent via Amazon SES, Amazon will report back if the mail succeeded or failed. In the event of success, Whoosh will place a green tick next to the email address in your imported list. Or a red cross on failure. The nature of Internet email means that sometimes a mail will appear to succeed, but will later be bounced, and fail to reach it's recipient. You can check for the number of these types of failures in the "Statistics" window. Some Amazon SES statistics do not get updated immediately however, so some failures may take several hours to become apparent.