How to protect your email from interception?
From this article you will learn how to securely encrypt your email, as well as make it anonymous (i.e. hide your IP address if you need to make sure that no one can find out who the email came from)
Email encryption using secure connections
Although this is the easiest way, it is at the same time very reliable. There is a secure version of the HTTP protocol (the language in which your browser and the web server communicate with each other), which is called HTTPS. Data transmitted over HTTPS is encrypted using SSL or TLS protocols. If your message is encrypted in this way, then it will be very, very difficult for a hacker to get to it, since for this he will need to decrypt it.

The easiest way to take advantage of HTTPS is to transfer all your email to websites that provide free mail services, for example, www.gmail.com or www.yahoo.com . You can use other mail services, but note that when working with a server that supports SSL encryption, the https:// entry should appear in the browser address bar instead of the http:// entry. If your chosen mail service does not use HTTPS by default, then go to the settings and find where you can enable HTTPS (SSL).

If you have to use an email client such as Microsoft Outlook, The Bat, Mozilla Thunderbird, Outlook Express, then you need to additionally configure it to work via a secure connection. It is not difficult to do this, but it is still better to use reliable websites that provide postal services, since their use is safer for a number of reasons. More on this later.

What should I pay attention to when using a secure connection? What are the risks of "information leakage"?
There are several ways to access your mail protected by a secure connection:

get access to your computer. This threat is irrelevant if you use a website that provides online mail services, unless, of course, you save passwords for accessing web mail in your browser (never do this if you want to preserve privacy!). If you use an email client, then anyone can copy your mail database and read it. To protect yourself from this, place the mail database on an encrypted hard disk partition, for example, using the VeraCrypt program. Read more about how to encrypt data in the article "How to securely encrypt the contents of your computer?";
get access to the mail server. If you use a website that provides postal services, then you are not afraid of this threat. If you use an email client, then this is a rather complicated problem. There are APOP and SASL protocols that protect the client's communication with the mail server from password interception. To use them, they need to be supported by both the mail client and the mail service server. Make sure that the mail service server uses these protocols. If you use e-mail at work, then your sysadmin has access to the mail server, and he will be able to read your mail anyway, so all the security measures discussed do not make sense to you;
choose a password to your mailbox. To avoid this threat, it is necessary to create strong passwords and store them in an inaccessible place. How to do this will be described in detail in the article "How to create a strong password?".
In conclusion, I would like to once again advise you to use online email services with a strong password, and if you still have to use an email client, then be sure to configure it to work through a secure connection and check whether the mail server supports the APOP and SASL protocols.