Found the addressing "Dy GM" in New Delhi area in the IT domain.
What does it mean?
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It means Deputy General Manager, also abbreviated as DGM
Citing sources, as requested.
Also, GM is an abbreviation for General Manager. Please see this Wikipedia link.
I work in IT industry, and in my company, we have positions like AGM (Associate General Manager), DGM (Deputy General Manager), GM (General Manager).