I have never heard of an ISP holding mail to send it all out at regularly scheduled times. But if they did hold mail until certain scheduled times, the difference would not always be exactly 5 hours; some mail might be delayed that, other mail, arriving later might, night be delayed 4 hours, 26 minutes, and others might be delayed less than an hour, depending on when it was received. There would be absolutely no reason for an ISP to delay every message the same length of time; this would remove any possible advantage of batching the mails.
Actually, the mail probably is not delayed at all; the receiving time stamp is more likely in error. To check this, have your parents send you a message, then check your mailbox a little later; I?ll bet the message is there, but with an erroneous time stamp showing it arrived much later than it did. If it isn?t present, keep checking periodically until it is there. It then would be interesting to check the Internet headers to see which servers it went through at what time, and how their clocks were set. If there really is a delay, it will be apparent here just where it occurred.
The exactly 5-hour difference in the two time stamps is a major clue. While your profile doesn?t give your location, I would guess your current time is Central Daylight.
Some Internet servers have their clocks on local time and some, such as my ISP?s POP3 server, are on Zulu time (i.e., Greenwich Mean Time or Universal Time). Universal time is exactly 5 hours later than CDT. So it seems as if the ?sent? timestamp may be local CDT, while the ?received? time stamp is Universal Time.
As an example, here is the tracking of an e-mail I received today. It was sent via Hotmail at 4:35:31 (16:35:31) MDT. A Hotmail server received it from the mail pickup service at 15:35:33 ?0700 (i.e., 3:35:33 PM Pacific Daylight Time) and forwarded it to my ISP?s server, where it was received at 22:35:33 +0000 (i.e., 10:35:33 PM Universal Time); this is when it went into my mailbox, and this is the receiving timestamp. However, before it appears in Outlook on my desktop, the UT is converted to my local time, 4:35:33 PM MDT. (Two seconds after it was sent).
This is a real puzzler. It would seem, then, that the receiving time conversion must occur at the receiving end. But apparently this problem occurs with everyone your parents send mail to, no doubt using different ISPs and different e-mail clients. I also assume that these recipients have no such trouble with e-mail coming from other senders. If all this is true, then it must be associated with your parent?s mail, but I haven?t figured out a scenario for the received time stamp to be in error based on an originating error.
However, if the receiving time stamp is correct, then the ?sent? time must be wrong, 5-hours early, if it is to indicate a 5-hour differential. This should be readily apparent. If you receive a message stamped about 9AM, then the ?sent? time must be about 4 AM. If you know your parents wouldn?t be up at this time, then the original time must be wrong, and the problem is with your parent?s computer or ISP.
Please perform the test I suggested in the second paragraph and let me know the results. Also, please verify that the problem occurs with all recipients, and that the problem occurs with no mail other than your parents. Then we may be able to track the problem further.