Some of it might be technical difficulties (yes, I've seen that happen a lot, both ways - emails go to SPAM, etc.) but also, you have to remember they don't often feel the sense of urgency that we might. Taking weeks to respond, especially when the wedding is months away, is pretty common. No response at all though, that's not ok in any business! Like you said, unless you've already exchanged emails successfully it could be a technical/email issue. To be safe, I'd call.