I have 2 users who monitor a third account's mailbox (nobody ever logs in with that account directly). Twice in the past week, they say that they've been checking the account for mail (they both have a proxy set up in GW 2012 Windows client) and seeing nothing, and then suddenly, hours later, there's the entire day's worth of email.

When I check the antispam (cloud-based) and GWIA logs, the messages have been coming in when they say they are. I also monitor a proxy account (a different one), and haven't noticed this type of thing happening, but I wouldn't tend to notice messages not arriving.

We upgraded from GW7 about 2 months ago, and this wasn't noticed until this week. Can anyone suggest what I could look at?