Hi there, Sincerely is a formal form generally used in formal letters and not so commonly used when writing emails. That is probably why you have not seen it. The same we can say about Faithfully, which is another formal form in letters. Hope this helps. Have a good day

I was taught in school to use: Dear … (his name), at the start, with Sincerely, (your name). at the end or Dear Sir, at the start, with Faithfully, (your name). at the end. .. for a formal letter. ('Regards' or something seems more casual/friendly) :)

I usually use "regards," in a business email or "I look forward to hearing from you," or, "Looking forward to hearing from you". If you are writing to someone you have an on-going business relationship with and you are equals it is not always necessary to have a formal closure at all. One way around this difficult formal/informal issue with emails is to have a signature setting on your email account that has your name, job title and all contact details. This does have the risk of seeming pompous or arrogant sometimes, depending on who you are writing to.