Modifying Email Storage Quota

Cache your kadmin credentials:

KRB5CCNAME=$(mktemp)
export KRB5CCNAME
kinit 'user'/admin

To administer the mail account settings:

cyradmin mail (or cyradmin sedna.astro.columbia.edu)

List current quota:

sedna.astro.columbia.edu> lq user.'user account'
 STORAGE 73266/1000000 (7.3266%)

Set new quota:

sedna.astro.columbia.edu> setquota user.'user account' 2000000
quota:2000000
sedna.astro.columbia.edu> lq user.'user account'
 STORAGE 73266/2000000 (3.6633%)
sedna.astro.columbia.edu>

Clear admin credentials:

kdestroy -c $KRB5CCNAME

Setting Global Email Message Size Limit

Currently the maximum file size for emails is set to approx. 50mb. To modify this value, edit the 'message_size_limit = 52428800' in the /etc/postfix/main.cf file on sedna.

Modifying Disk Space Quota

see ​debian-administration.org for some reasonable tips.

To modify a user's quota:

edquota -u 'user'

An editor will be invoked for editting of the soft/hard limits. 
Quota will be updated after saving/exiting the editor.