no explanation needed.

'Dost/dosth' would mean 'friend' in English. Another word in Hindi for friend is 'mitra'. However, the word 'dost/dosth', like friend, can also be used in the sense of 'companion'.

If you meant 'dosth email' or 'email dosth' then it would obviously be 'email friend' or 'email pal'.

Best wishes
Roomy Naqvy