I would guess it means Engineer. How you write to him depends on what is usual in that country.If you don't know him then Dear Mr Fattah (assuming Fattah is his family name) is probably correct. Possibly Dear Eng Fattah if Eng is used as a title like Mr,Mrs,Dr, Prof etc.

I have never heard of it, and even when I looked it up, I couldn't find it in any of the regular lists. If it is engineer, then it would usually have some other letter with it to say whether it is Bachelor, Mastor, Doctor or something else. Another possibility is that it was typed wrong. Maybe it was supposed to be Gen (General)? Or it might be short for English, and it is saying that is his name in English? Or it could be another name that has been shortened because it's a long but commonly known name in that area? I would say most likely is that it is short for Engineer, as GuideDogSaint suggests, and that it is just something they do in some countries (which I have seen on another forum someone said they do use Eng for Engineer in his country, but he didn't say which country). But whatever the case, I think the safest thing to do is use Mr Fattah.