Step 1: Estimate the total population of India

India's population is approximately 1.4 billion.

Step 2: Estimate the percentage of the population that uses the internet

Roughly 50% of India's population has access to the internet. This could be higher now, but we'll use this figure for our estimation. That gives us approximately 700 million internet users (1.4 billion * 50%).

Step 3: Estimate the number of these who are in the workforce or education

Microsoft Office 365 is typically used by working professionals and students. According to various sources, we could assume around 40% of India's population is part of the workforce or in education, either formal or informal. So we have approximately 280 million potential Office 365 users (700 million * 40%).

Step 4: Estimate the percentage of these users who would likely use Microsoft Office 365

This is a difficult estimate because it depends on many factors like the prevalence of Microsoft software in businesses and schools, the popularity of alternative software, and individual choices. However, for the purpose of this estimation, let's assume that about 40% of the potential user base actually uses Office 365. This is purely a hypothetical assumption for the purposes of our calculation. So, we have around 112 million Office 365 users (280 million * 40%).

So, based on these assumptions and calculations, the guesstimate for the number of Microsoft Office 365 users in India is around 112 million.