We’re currently having a problem with delivering mail to the push.boxcar.io domain. This domain is used for push mail notifications for iPhone users, so as a result iPhone users may not receive timely notifications of new mail at this time.
Mail delivery to this domain is currently suspended since while their servers are refusing mail to avoid confusing errant bounces being generated.
Note that this has been an ongoing issue over the last few weeks and the problem may occur when not specifically mentioned here. Also note that the problem isn’t on our side, so unfortunately we don’t have any further information or an estimated time to resolution at this time.