Hi Connie.  You would use the SetRequestedUserSettings.  The string that you want to pass along is 'servicelevelmap', using the below values.  For example, I tested this API call, and passed along servicelevelmap=30.  That disabled POP for this user.  

If you would like to disable POP, IMAP, and SMTP, then pass along the value of 16 (which leaves access to the web interface enabled).  I hope this helps.

 

• servicelevelmap (The enabled services for a user. This field is a bitmap composed of 1=POP, 2=IMAP, 4=INCOMING SMTP, 8=OUTGOING SMTP, 16=WEBMAIL. For example, to set POP and IMAP, the value of 3 would be passed.)