I don't think it sounds douchey, but I would prefer if someone ended their letters with,

"Cheers, and let it be known that I specifically mean 'Cheers' the 1980s American sitcom starring Ted Danson, Shelley Long, and in later seasons Kirstie Alley."

I think 90% of e-mail etiquette is bullshit anyway so i don't mind a "cheers"

I say "all my best," if i feel like being cute and polite. I do "best," or "thanks" or just sign off with my name if Im lazy. If it's someone I have a good relationship with and i straight up do not care to perform email etiquette then I put my entire message in the subject line (if it's short)

When I see 'cheers' it just makes me think the person is British. I don't really like it, and I would never use it myself, but not sure if it's douchey per se. I usually end my emails with 'thanks' and then sometimes my name, but then, I guess most of the times I send an email I'm requesting something.

It depends on the reason for the email— Most of the time I write emails to clarify or request something. I usually end with Gracias or Thank you. I don’t often write personal emails.

It really depends. Cheers.

No. I don't write emails.

Regards

Depends if it is a private E-Mail message or chitchat or something official. I might even use cheers too as this is very common in German.

If it’s formal: regards. If it’s friendly: P.

Nah it's fine, my understanding is that it's the equivalent of 'thanks' and I close with thanks all the time...of course, I'm also a douche so maybe that tracks after all