Indian English is closer to British English than American English, so if you specifically want it to be in Indian English but don't know that yourself, I'd use British English.

But unless you have some special reason to believe that it's important, I don't think it really matters. All of the forms are pretty understandable by everyone else. I can tell that someone using British English isn't from here in the US, but it's not really an understandability problem. Long term, my guess is that they'll just blend together due to international interchange anyway.

Maybe if you're a professional journalist in the US and the publication you work at has specified American English in their style guide, they might care about your ability to specifically do that, but I can't believe that there are many positions that would. I've worked with people who use British English on the job in the US.

The only specifically-Indian English word that isn't present in other forms of English that I can think of off the top of my head is "prepone" -- that is, to move to an earlier time. It's a riff off "postpone", to move to a later time.

Just do the needful when intimating with the recipient.

Kidding aside, you need to provide more context. Is the reason for using indian english for the recipient to understand you? In that case you don't need to, they should understand you fine with US conventions. If your intent is to act like a local, which I don't know why you have to, try googling sample emails and go from there.

Definitely start with "Good Sir", that's what I learned from years of reading voLTE requests on xda

When I think of all the shitty emails I've received from all over the food chain I'd say it doesn't matter. Getting your point across is much more important than imitating a specific culture.

And seriously, badly imitating some conventions is much much worse and insulting than using a phrase that might not be familiar to your audience.

Just write it. US or UK doesn't matter.

Ok I'm British and I don't get this. Yes there are specific turns of phrase or idioms that are different in British/American/Indian but really, is anyone who can actually read and write going to stumble on them?

Example of British English (since I'm guessing most readers here are American): "oh, we suggested Wednesday by accident, shall we meet on Thursday instead". Is anyone really going to struggle with 'translating' to "oh, we suggested Wednesday on accident, shall we meet Thursday instead"

Largely it's going to depend on who your audience is. If you're writing for an American audience, use American conventions. British audience, British conventions.

Things to be aware of:

Date formats:

US: 5/6/2024
British/India/Australia: 6/5/2024

Currency formats:

US: $1,234.56
Europe reverses that, so €1.234,56
https://www.ricksteves.com/travel-tips/trip-planning/european-numbers
India: https://en.m.wikipedia.org/wiki/Indian_numbering_system

That's above and beyond things like Metric conversion which the US largely does not use except in soda bottles. 1, 2 and 3 liter bottles.

Spelling:

In the US, it's "color", in the UK it's "colour". There are LOTS of examples like this.

https://en.m.wikipedia.org/wiki/American_and_British_English_spelling_differences

If you have a choice of conventions, ie you know how to implement these three kinds of English, then my recommendation would be to adopt the style of the audience of the email.

If the guy is British, use British English. If he’s Indian, use Indian English. If he’s American, use American English. When able, it’s simply polite to use language best suited for understanding by your audience.