In case you suspect someone is intercepting your email correspondence, there are steps you can take to make sure that your emails are not compromised:

Use PGP to encrypt emails - Emails can be encrypted using PGP (Pretty Good Privacy), which is based on public key cryptography. You need to generate a key pair - a public key that you share with others and a private key that you keep secret - to exchange encrypted emails with correspondents.

If you use an email provider like Gmail or Outlook, you can encrypt your communication using Thunderbird, an open-source email client with built-in OpenPGP capabilities, or by using the Mailvelope browser extension which works with popular webmail services. By using these tools you can easily generate a key pair for encrypting your email, or import existing encryption keys.

Switch to encrypted by default email providers - There are email providers, such as ProtonMail or Tuta, which encrypt messages automatically when they are sent between their users and also provide ways to send encrypted emails to those using other providers. Please refer to these Proton and Tuta guides on how to send password protected emails to users on other email providers.

Change your email account password and turn on multi-factor authentication - If you suspect that someone has accessed your email account and has been reading your correspondence, change your password immediately and set up multi-factor authentication (MFA). MFA adds an extra layer of security by requiring a second form of verification, such as a code sent to your phone, in addition to your password. Please refer to this guide for details on how to set up MFA on multiple email providers. 2FA Directory has more information on which tools support MFA and links to guides.