If I delete a bunch of emails from outlook, can my manager still retrieve them and read them? If yes, can they view all the attachments?
If you're using Exchange Server then yes, this is easy, any deleted item(s) can be restored by authorized person including attachments within the retention period.
TL;DR: Can they? Almost certainly. Will they? Usually not, unless you give them reason to or they're a particularly bad workplace.
If the emails were there for any length of time they could easily have been caught in the backup cycle and therefore be retrievable in the event that anyone had a reason to suspect you had deleted something that might be important.
If you were being monitored then it would be possible for your IT department to forward copies of your emails to someone else without you knowing. It is also possible that your boss could have been given access to your email if you were under investigation for misconduct.
Because you used company property whatever you sent could have gone through any number of systems. Firewalls scanning for corporate secrets, virus scanners, and data protection systems could all have caught a copy or at the very least taken the subject line and a brief excerpt of the email.
Even if your company provides "free" WiFi as a courtesy this could easily be monitored and logged. Emails used to be sent in cleartext so anyone could read them if they wanted, thankfully encryption is more common in email clients now.
The thing here though is that in most countries giving this level of access would be considered unethical and potentially illegal unless some kind of disciplinary proceedings were under way. I would consider it "against the norm" for any workplace to attempt recovery or otherwise monitor employees without due reason. I have heard of places, but those places tend to have Banana Dictator Managers with little regard for the meat-sacks that litter their office and a high employee turnover as a result.
On the bright side, backups often get recycled or purged, logs get erased after a while and people forget.
Unfortunately, anything you do on a employer laptop is considered property of the company. I'm sure you signed some sort of agreement when you started, indicating your laptop is the property of the company.
Even if you deleted the emails, your organization most likely will have a comprehensive backup strategy in place to recover anything deleted, even from several weeks back.
There are multiple ways that email can be retained separate from a backup. The most common is called Journalling and it has nothing to do with Outlook. It merely duplicates all incoming messages and stores them in a secured place. This ensures that if the company is sued, etc., that it has a record of every email sent and received by the company.
In short, you should assume that every email you send or receive, every web page you visit, every porn file you download onto company property will be documented somewhere. As many of the others have stated these are rarely used unless there's a lawsuit or Intellectual Property at stake.