When a preview mail is sent, it always get priority to be sent as soon as a mail server is ready to send it, it should not take more than a minute before it is sent in a worst case scenario.

What I'm wondering is whether there could be any grey-listing or other mail filtering application at the receiving end that could delay the delivery? If you could get back to us with examples of what previews this occurred with (time of sending and what account that was used), we can trace this and solve the issue or advise you what steps to take to avoid this.

Please register this as a support case at http://world.episerver.com/Support/Register-Support-Incident/ so that we can track the communication and so that you can supply us with the account information in question.

Thanks in advance!