inbound email does not pick emails from all accounts.

hello I have 15 inbound email accounts including the bounce mail account, so 14 of them are creating cases assigned to different persons…
some accounts are not fetched regularly, like if the job would timeout or the process would hang on another email .

most accounts are serviced but one or two are serviced only about 4 times a day.
the normal job run every 10 minutes.

my environment is php 5.6 running on IIS and mssql2012 database.

So the problem is really intermittent… by the same toke how can I check or change the order that those are serviced?

Any idea?