There are a number of issuing Authorities from which you can obtain security certificates for use either with secure web pages (if you have your own web site) or to use with your email program to positively identify to recipients of your emails that the emails actually came from you and do not have a fake return address. This latter use is becoming more important with the increasing number of spam emails and emails with viruses attached that generate both the from and too email addresses.
Most likely if you require a certificate for web page security you will have to pay for it. Some authorities require that you pay for email certificates as well but some make them available at no charge. With such free email certificates there is not likely to be any checks done by the issuing authority to confirm who you say that you are but they will confirm your email address by sending an email there that contains the link that you need to use to access the web page to actually provides you with your certificate. Your would need to use that link to actually get to the certificate which confirms that you have access to receive emails at the specified email address.
You may find that the issuers web site is set up to use Internet Explorer proprietary processing to actually transfer the certificate to the certificate store built into IE so you may need to use IE to apply for and obtain the certificate even if you usually use a different browser.
Once you have the certificate in the IE certificate store it is then a simple matter of exporting the certificate from there and importing it into the email program of your choice. To do this you need to go to the Tools menu and select Internet Options. The security certificates are not found on the Security page as you might expect but are found on the Content page. The Certificates button is about half way down. The certificates that you have obtained should be found on the Personal page of the Certificate Manager. If the email program that you are using does not already have copy of the Intermediate Certification Authority or Trusted Root Certification Authority certificate(s) then you may need to transfer those as well but you will need to export the certificates one at a time.
To export a specific certificate you just select the certificate and then select the Export... button. This will start the Certificate Manager Export Wizard that will take you step by step through the process of exporting your certificate into a standalone file which can then be imported into your email program.
This article written by Stephen Chapman, Felgall Pty Ltd.