What is the procedure for notifying editors of abusive mail? I know that editors see corrections and associated answers, but what about mail which is sent by 'send a message to'? If the offensive mail is left in your personal mailbox, can an editor look at it if invited to?

Yes, administrators can have a look at the offensive message. So please leave them in your mailbox as evidence if you ever receive one and alert an editor or administrator.

It helps if you give details of the person sending the mail, name etc. In fact copy and paste the message and header to us.

I have in fact received a mail message which is offensive, however my pc skills are poor so I wouldn't have a clue how to 'copy and paste it', nor indeed do I know to whom I should send it, or who I should notify. Will any editor do? Who are the administrators anyway, are they the same as the moderators?
I'm not too worried about abusive mail, preferring to ignore it, but it could be that senders of such make a habit of it, and may put people off the site altogether.

Here's a list of all administrators, editors and moderators. Alerting an administrator is the most efficient way to go, but any editor will do, since they'll pass on the message. Even though the forum moderators may be editors as well, the forums are a different part of the site and moderating is something else than editing. Hope that helps.