For some PP Express transations email is not sent

Why is it that for some type of Paypal Express transactions email is not sent. I can't pinpoint which transactions exactly because I can't detect a pattern. Most email is being sent to us, each with a number from the ID on the database, but I see some few numbers are skipped on the emails sent, although the transaction IS on the db and on Paypal. Is anyone aware of some type of Paypal Express transactions in which email is not sent? I think we are getting all the Paypal Direct transactions' email. Any feedback on any known issue regarding this would be appreciated.

You might want to look into your email server logs.

I would imagine it would have to be because of the email failing to be sent by the email server. Since you get some emails it would seem that the scripts that tell the email server to send the email are probably all working, so it would have to be that the email server isn't sending the email, or the emails are getting spam blocked and are being sent and you just aren't receiving them.

I doubt it has anything to do with express checkout directly.