There seems to be major delays (30 minutes or more) in receiving test messages right now.
I'm having the same issue - on the mailbuild side in the middle of one of my clients trying to send a time-sensitive campaign!
We are aware that in some cases previews are slow going out, and we are addressing this with new hardware, but unfortunately it takes time to setup. Also, keep in mind that email is not an instant medium, and there can be a lot of mail servers between us and you.
Even when we send the preview instantly, a slow mail server in between can mean the email does not arrive for some time.
This is not meant to be an excuse, just an explanation of how email works. We are definitely working from our end to make sure we do send those previews instantly.
I'm having the exact same issue. It is difficult to promote using Campaign Monitor when clients don't receive things for ages and frustrating when trying to test things.
It never used to be this slow, getting previews did used to be pretty instantaneous and its only in the last few weeks or so I have noticed a distinct slow down.
Hope it gets resolved soon.
Experiencing delays of up to 20 minutes on test emails here too. During my first campaign (a week ago) I was receiving test emails almost instantly.