Due to the problems that Pine has with reading and writing message to a Maildir formatted mailbox, We would strongly recommend that you switch to the 'mutt' mail reader. Mutt is much more flexible and a whole lot faster. It's generally just better. If you decide to stick with pine please note that none of the messages in your pine-sent-messages folder will be viewable from your WebMail setup. This is because pine can't copy sent messages to a Maildir formatted mailbox. But Mutt can.
Using Mutt should be pretty straight forward. At least I think it is. It will take a little bit of time to get used to the keys that you must press to run different parts of it, but once you do you will be happy. Mutt is basically split into two or three windows depending on what mode you are in. When you first start it up you will just see a list of messages in your INBOX. You can use the arrow keys or j and k keys to move up and down the list of messages. When you want to view a message, hit return. When you want to get back to the list of messages, hit i.
If you want the folders that you use and create in mutt to be viewable from Squirrelmail(Webmail system) or the IMAP server you will need to prefix each folder name with a '.' (period) character.
To compose a message just hit the m key. Doing this will prompt you for who you want the message to go To: and the subject of the message. After you type in the subject Mutt will spawn off pico so that you can compose your message. When you are done, exit out of pico with Ctrl-X and choose to save the file to the default path. Now you'll be in a window that let's you make final changes to your message before you send it out. From this view you can add and remove addresses from the To, Cc: or Bcc: lines, change the Subject: line and so on. If you want to re-edit your message, type Ctrl-x-e. It's really not that hard to get used to.
Once you are done making modifications you can either send your message out by hitting the 'y' key or you can hit 'P' to postpone the message.
You can add address aliases (like an addressbook) to your mutt configuration by editing the .muttrc-aliases file in your home directory.
If you ever get lost you can always hit the question mark key '?' to get onscreen help. Also, the menu at the bottom of the page usually gives you the most commonly used commands in each view. If you need to know more information about using Mutt, you can visit the online Mutt manual.
Check out the .muttrc and .muttrc-extras files for more configurability. Mutt can do just about anything.