Greeting- I wouldn't say 'to my' as you are talking directly to them. Also 'fellow colleagues' is a bit of repetition, isn't it?
YE had provided- without knowing what YE is, I can't be sure about the tenses used here, but imagine that the present perfect might be better here.
solid platform of learning- I'd say 'for learning'
Skills that I had embraced while working for YE- again the tense- if you still work there, then use the present perfect and replace 'while' with 'since'
My confidence had improved dramatically- has again iof you're still there