Recently, I got hit by change in Google policy regarding self-signed certificates (see their FAQ). For many years I’ve used self-signed SSL certificates for my company’s server (f**k giving money to the CA mafia ;)). As some of us prefer to use Gmail over crappy desktop clients, they used Gmail Mail Fetcher feature… until it stopped working.
But there is a great site https://www.startssl.com/ with free Class 1 SSL certificates (see comparison). It’s dead easy to create one. They even check your configuration automatically afterwards. Not being an expert I screwed it up a little and got an email with warning: “It seems, that the installation of your server certificate […] is not complete! You should add the intermediate CA certificate to your installation”. They pointed me to their FAQ where I’ve found instructions how to configure Apache server. Then it was easy to do the same for mail server.