What do legit journal/conference/review invitations look like? As everyone else here probably does, I receive a lot of unsolicited emails. I don't like it, but I've gotten used to it and can just ignore them with a friendly smile on my face, because at least those emails give some unfortunate person a job and an income.

However, today I got an email that at first seemed undesirable but at a second look appears to be legit (albeit irrelevant, so I wouldn't have missed anything), so I'm wondering if there's any rules or hints to go by to identify legit conference invitations or journal introductions?

On the one hand, this is probably going to be simply somewhat of a reverse of identifying undesirable emails (see below) but I guess I'm mostly looking for information on how legit entities advertise themselves. Do they:


actually send out unsolicited emails at all?
invite "unknown" researchers for high profile roles?
even care if they emails look legit?


I'm a geoscientist (sorry, we hit rocks with hammers and trample on vegetation, but I'm working to better myself), so I have been at conferences organized by AGU and EGU, so I do get emails from those two and they're legit, but for example AGU doesn't care about the third point at all, with their emails being a mess of HTML with embedded (and thus of course blocked) images and obfuscated links with over 100 chars of tracking stuff in them, so if I did not know they were legit, I'd long have added AGU to my list of undesirable publishers.

And the second point, well, like most early career scientists, I have a slight case of impostor syndrome, but I probably have some good stuff out there and apparently I'm a good speaker, so it's probably not impossible that someone saw me at another conference and thought "Yeah, I'd like to have that person as a speaker", but is that really how it works?

And just reversing my criteria for spam is probably also not a surefire way to identify them. Sure, a  poorly formatted email in poor English to "Dr. JC_CL, Coauthor and Coauthor, I hope this finds you well" from a Chinese company I have never heard of for a field not even related to what I'm doing can probably be disregarded. However, all of those errors could also happen in a legitimate case, as my name is somewhat complicated for people not speaking my language, most people don't speak perfect English (and I can't identify perfect English with 100% certainty) and I do work quite interdisciplinary.
The #1 criterion is: they come from someone whose name you recognize as a respected colleague in the field. Or, at least, a conference or a journal that you know already.

The #2 criterion is: they look like they are not written automatically. Compare


  Dear Arthur, I have seen your very interesting article on shiny rocks and I would like to invite you...


and


  Dear A.Uthor, I have seen your very interesting article Shiny rocks in South African Mines: a Case Study and I would like to invite you...


The second one seems auto-generated, since they copied over your name and title verbatim. The first one looks like someone went through the effort of paraphrasing the title into a real English sentence.

In my opinion also putting a lot of emphasis on proceedings, Scopus and ISI-indexed journals and impact factors is a red flag. This is something I would never mention if I were inviting a real person to a conference.