If your organisation uses Nokia phones, then by default, a stock 10.6 mail server will be pretty much useless. Even with some fairly recent hardware (E72), the phones won't be able to send or receive any mail. Here's how to make it work:
Enable PLAIN authentication for IMAP, POP and SMTP. This isn't such a big issue if you're using SSL. Some Nokia's might actually do CRAM-MD5 off the bat, but sooner or later you will run into a user who can't log in.
Enable “SMTPS” support in Postfix. “SMTPS”, on port 465, was a “brilliant” Microsoft idea to start using port 465 for secured SMTP connections after they apparently couldn't get Outlook 2000 to work with port 25. They just missed the fact that 465 had already been assigned to another protocol by IANA. What's fine for Microsoft's fine for Nokia, unfortunately, changing the mail client on a mobile is a bit more difficult than moving your poor Outlook user to Thunderbird, so:
sudo nano -B +30 /etc/postfix/master.cf <uncomment lines 30-33> and save sudo postfix reload
And also don't forget to forward tcp/465 to your mail server in your firewall.