My wife received an iPhone for Christmas this year, and she's been having fun playing with her new toy. She was very excited to find out that she could check her mail from the phone, and as I had never bothered to set up mail on mine, I took a few minutes to set her up. But, this simple exercise took a bit longer than I expected, since my mail server here wasn't set up for this just yet.
I have both POP and IMAP configured, but haven't tested IMAP extensively, and have only used it via the webmail apps I run, and the iPhone was trying to talk on ports that I hadn't set up yet.
The first order of business was to allow mail to be received on port 587, this is done by uncommenting the line starting with #submission in the postfix master.cf file. The submission port is a standard designation for port 587. If you would like to have postfix be able to receive mail on other ports, simply copy/paste that line, and change the word 'submission' to the desired port number, restart postfix, and postfix will now be listening on this new port. This may be handy for getting around certain networks that block the standard mail ports and want you to use their mail gateway. Having an alternate port you can send on may be handy to have in those rare occasions.
The next trick was editing the account setup on the iPhone. After entering all of the account info, the initial connection failed. I began tweaking settings on the mail server, but couldn't easily get back to change my wife's account setup on the phone. I found that by going to the phone's Settings, then Mail, I could select the account, and at the bottom of this screen was an Advanced option, that let me tweak all of the settings.
Despite declining to use SSL encryption, this option was still selected for both incoming and outgoing, very simple to turn off. This screen also lets the default ports be overridden, again, useful to get around certain network blocks.
Once I had tweaked the necessary settings on the iPhone, I had her mail running just fine. Thank goodness for unlimited data plans...