Can workflow validate that an email was sent without any issues? I want to make sure the email address is valid, but I'm not sure if workflow has that ability.
You can set the Email activity to request delivery receipts:
I'm not sure if all email servers support this feature.
It depends on your email server because Workflow doesn't send the email directly. In our environment, the Exchange server kicks back an error message if an address is forbidden or doesn't fit the required email format, but that's about it.
The idea is that Workflow sends the email to the email server, but it doesn't get anything back beyond the initial verification. The server simply tells Workflow whether or not the email was successfully sent, not whether or not it was received because that happens after the fact.
Think about when you email a bad address. Sometimes the return message about it being an invalid address won't come back for more than a minute and you wouldn't want your processes sitting around waiting for something that may or may not happen.
The crazy workaround version might be to see if you can send those with a known Reply To address, and have your email server forward any return messages to Import Agent. As Jason said, you aren't guaranteed to be notified if there was a problem, but on the off chance that you do get an error, you might still be able to capture it.