Many thanks. I'll take a look at that book, I haven't gone wrong with No Starch Press yet. Edit: For anyone else who is looking and can't find it on NSP's webs

Many thanks. I'll take a look at that book, I haven't gone wrong with No Starch Press yet. Edit: For anyone else who is looking and can't find it on NSP's website, I found it with 'filetype:pdf The Book of Postfix' on duckduckgo.