Sebastian,
First look in your sent items folder, this is where you can check the status of any outgoing items. If there is an item you tried to send but the send didn't happen the item will be flagged with red flag icon.
Second, if there is nothing obvious in your sent items folder check your pending requests: "Accounts | Pending Requests". Is there anything suspicious there? NOTE if you delete a pending request that item will not be sent and you'll need to resend it.
Scott