Well, this time I did get a timely answer! Not sure that it is really helpful as none of their emails is going to my spam folder - they are just not sent at all to me as far as I can tell.
"You may have noticed that you are receiving fewer BonusMails than you did prior to our new website launch. Because we have introduced new technology, we're ramping up the number of emails slowly in order to ensure the highest level of performance. Rest assured that BonusMail will be back to its normal levels shortly.
For some members, BonusMail is being inadvertently delivered to "bulk" and "spam" folders. In an era where non-solicited email has become increasingly burdensome to our members, we applaud the efforts of email providers to keep only the email that you want in your primary inbox. Unfortunately, when email is not immediately recognized — as is the BonusMail from the new website — we must allow the email filters to adapt to our new format."