Why do they address me "Dear (surname)"?

I have a little international business contact, and sometimes, some people write me a mail and address me as "Dear (my surname)", no "Mr", no nothing. Where is this common and how so? I never knew this. I only know "Dear (first name)" (American) and of course "Dear Mr (surname)", as well as "Dear (first name) (last name)". But this new variation, I can't quite grasp yet. Your input would be appreciated.

Solution 1:

I see two possibilities: the first is that your correspondents come from one of the few social circles where Smith is a common form of address, and hence Dear Smith a common salutation. I haven't been in one such since my schooldays, but cultures vary.

Or it may be that the only information available to them is your surname, since somebody in the hierarchy is frightened of seeming sexist by providing gender. In such a case, Dear Mr, Miss, Mrs or Ms Smith would be even less friendly than the correct Dear Sir or Madam, so Dear Smith may seem a reasonable compromise.

See also How should I address someone with a known name and unknown gender?.