There are many reasons why email messages may not succeed in getting through to the intended recipient. These will generally result in your message being returned to you, probably from an address such as 'Postmaster' and with a subject heading like "Delivery Report (failure)". The message will have a lot (at times, an awful lot) of computer-generated messages, hidden somewhere in which will be the reason for the failure.
It is not possible to cover all reasons why email messages may fail, but the more common ones are described below, together with any remedial action you can take. If you are using Nexus and get an error message when you send a message, take a look at the Interpreting failed-delivery reports page.Sections in this document: