I did a search online already and no one who answers has a real understanding or explanation and most importantly, a solution. That is probably because it doesn't happen to the people who answer in particular. But I find several examples of people asking the question, so it is something that does happen.
This continues to happen. It is not an exception. A friend and I communicate often, in fact daily. Sometimes the e-mails go right through, sometimes it takes hours or even a day or so for the e-mail to make it into the in-box.
thanks for your question!
It can happen that emails get delayed for various reasons. e.g. AOL often refuses emails from various sources for "possible spam" first and if the sender server sends a 2nd time then it's getting passed on to the receiver, else it's considered spam (as spammer servers never retry if it failed the first try on delivery).
It could also be that the receiver server was down for the time the email was supposed to get delivered. some providers then try resending it another time after 24h. some providers try this 5 times to deliver the message, hence it can take 5 days until you get an undeliverable notitce.
And another positibilty ia slso that the destination receiver was just too overloaded for processing the email.
Sometimes sending an email with wrong time and/or date can cause troubles too.
Those are all things you cannot influence at all
I especially noticed this when receiving emails from AOL, Hotmail and Yahoo mail.
Hope this gives you some insight!
All the best!