How to detect Keyloggers on iPhone or Mac

There simply is no logical way to guarantee the absence of keylogging software. There are only ways to determine the presence of certain, known key loggers; and even if you were to confirm the presence of a well-known one, it could have been installed in an effort to distract you from the presence of some lesser-known one more difficult to detect or eliminate.

There are a number of ways an email account can be "hacked" ranging from the mundane (looking over your shoulder, or having a surreptitiously installed camera aimed at your iMac's display) to literally guessing common passwords, to very popular and extremely successful phishing scams, to highly sophisticated means literally impossible to detect. The latter possibility is not even worth considering unless you are a high profile target of an investigation from entities with essentially unlimited budgets (federal law enforcement agencies for example).

You might be able to determine the presence of common, well-known keyloggers by examining certain macOS system folders. The easiest way to do that is to download and run EtreCheck, which you can read about here: Using EtreCheck. Post its report in a reply to this Discussion. Just beware that even if you were to find one, eradicating it is probably not something you should consider, because that Mac would be considered evidence in a criminal investigation.

Other ways of lifting your personal information might involve snooping on your wireless network. Protecting yourself from that possibility requires protecting your wireless network and all its equipment both physically and with secure passwords... with emphasis on both the wireless network and all its equipment. Anyone with physical, hands-on access to your Mac or the router(s) it uses can use a variety of techniques to eavesdrop on what you're doing.

Really, the first thing you should do is to ask yourself who might be interested in "hacking" your personal information. The usual suspects include future former spouses... etc. Unauthorized use of a personal computer is a crime and has been for many years, so if that's your concern you need help that goes far beyond the scope of this technical support site.