WordPress currently doesn't support blog by e-mail via POP3 over SSL. This is especially a problem for Gmail accounts since they won't work over regular POP3 (non-SSL). Also, having SSL is always a bonus as far as security is concerned.
This feature would be REALLY nice to have.
I've seen a few proposed workarounds for this, including using Postie and wp-gmail.php. But neither seem to be supported/updated anymore, and I couldn't get them to work.
In reference to the last posts on both: simply using ssl://pop.gmail.com as server address doesn't work. Since there's no SSL support in WordPress, you just get an error from Gmail's server.
Blog via e-mail is ridiculously easy in Blogger, but I really like WordPress. It would be nice to see this implemented in WordPress so you just put your account name, server, and password and you have instant blogging (text & images at least) via secure SSL e-mail for easy mobile blogging.