Its been a few years since I dealt with that type of thing personally at VF and things may have changed. Having said that back then examples with dates and times could be  taken by the tech team and passed on to be checked. In all the times I did an investigation I think I personally only ever came across one case (excluding know widespread faults) where a customers emails were blocked and it was because the sending server had a bad rep.

I have looked into this for a couple of friends who were unable to do a password reset for one of their suppliers websites, and the problem was a web server that was directly sending from the websites IP address, when the domain was all set up with SPF for their hosted email server and a really bad reputation for their web hosts shared IP address. Not a fault with the receiving mail server when the senders are doing dumb stuff like that.