Usually if an e-mail is genuine it will have the company¨s name somewhere in the e-mail address - if it does not, don't open it, but move it to your junk folder.
Private e-mails should end on one of the e-mail services we all know - hotmail.com, outlook. com gmail.com etc. If it doesn't don't open it.
Don't click on links if the e-mail tells you, your visa card has been or will be annulled or your subscription to this that or the other - these are all scams, as like as not.
No country's Inland Revenue sends anything by e-mail, nor do banks, insurance companies, government offices etc.
Apart from using common sense, it is wise not to be in a hurry when checking your e-mail - take the time to consider whether you know the sender.
Any domain calling itself xyz.com or the like is bogus, so read the entire sender's address.
Likewise if you never have heard of MarvellousBargains.com it is because I made it up right now - my point being that anyone can call themselves anything they like, but that does not make them a reliable company.