If at first you don’t succeed, try, try again. Then give up. There’s no use in being a damn fool about it.
– W.C. Fields, early 20’th century actor.
SMTP servers will do their best to deliver delayed email over the Internet, and will generally keep trying for several days. For example, occasionally you will receive an email with a subject something like the following:
Warning: message 129iHc-0007Z0-00 delayed 24 hours
The message body will also often say that the email you sent hasn’t been able to be delivered, and usually that the system will keep trying. Usually this means that the email server at the addressee’s end is temporarily off-line for maintenance or because of some termporary system problem.
You can safely ignore these sorts of messages, and your email will usually be sent through when the problem is fixed. However, if you receive another email that says that your server has given up trying, then you should check with the addressee by telephone to see if their email address has changed or if their system is having other problems.