E-mail is Never Late

This can be a difficult concept for people to understand sometimes, but, e-mail is never 'late'.  In the world of electronic mail, there is no expectation of a delivery time.  Well, end-users perhaps expect that it shows up where they expect 'immediately,' perhaps, but shouldn't.  Instantaneous delivery is prevented by simple physics, although, it may seem at times like delivery is close to that.

Once again, perhaps, this goes back to the way the e-mail system grew up.  Originally, much like the US Postal Mail system, e-mail would be queued and sent in batches (or, put in a post box, picked up by a mail carrier, and transported en masse).  From the time you press send, your mail (typically) goes to an intermediary mail server which delivers mail on your behalf.  Your mail may be sent as soon as it is received by your mail server.  Or, it may get queued for any number of reasons.

You may note that this tends to happen with the high-volume mail services, such as Yahoo!Mail and Hotmail, more often.  Both inbound and outbound.  AOL's mail servers will also temporarily reject your mail if you've sent too many messages within a given period of time.

One reason for queueing is to prevent stampeding.  If this particular mail server has many, many messages to send to a particular domain, it should throttle back send there as to not overwhelm the receiving system.  That's a good thing.

Sometimes an e-mail message may make several stops along the way.  Sometimes this is a stop at a virus/spam scanning box that then moves your mail along.  This makes for a delay under the best of circumstances.  Attachments don't help.

This is all to say that the "send" button is not connected directly to your recipient's inbox.  If it's really important, and you need to get a message to someone, pick up the phone.  You'll know immediately if you've made a connection.  Plus, it'd be nice if you took a minute and asked about their day, kids, spouse, whatever.  Let's not always be in such a rush!  Just remember: e-mail is like life in general; there are no guarantees.