The thing is that Opera is using big part of fastmail code, even parts that are not official implemented yet. These parts are not accessible from current Opera E-Mail UI, but there is a trick how to access them.
The first step is to log in on mail.opera.com.
Second step is the cool part. Put this URL:
to you address bar and change the XX the to one of the following:
AA, BB, BG, BU, CA, CD, CF, CH, DL, DR, EG, FI, FL, FS, GC, LP, MC, MI, MS, NP, PE, PL, PM, PY, QU, RA, RS, SG, SU, TI, TV, UA, VD
Each of these signals show you different secret dialog. Some are more useful than others and some are not useful at all. There is a simple description of each signal:
The interesting (for me):
BU - "Bandwidth usage"
FI - "Define Rules" .. Filters <3
FS - *Files* .. You can upload some files to your account. The quota is 10MB. Uploading files is possible, but some other parts like public site to download them is not working.
NP - *Notes* .. very simple, it would be awesome if it was connected to Opera notes.
QU - "Quota usage"
RS - "Referral Status" .. I'm not sure if this is working, can you please click on this link?: http://www.myopera.com/?STKI=5864829
AA - "Add to address book" .. Adds e-mail addresses from sent e-mails to your contacts. Opera E-Mail is doing it automatically so you don't have to care about this one.
BB - "Buy Email/File Storage Bandwidth" ... It is not possible to buy more E-Mail bandwidth .
BG - "Buy Gift Certificate" .. Not useful, you can't buy Gift certificates You have to find another gift for your parents for Christmas
CA - "Cancel account"
CD - "Custom DNS"
CF - "Edit Custom Fields" .. Something with fields for contacts
CH - "Add Funds" .. Again, it is not possible to use payment actions
DL - "Distribution Lists"
DR - "Domain Registrant Information"
EG - "Edit address groups"
FL - "Folders" .. Use Opera UI for editing folders instead
GC - "Retrieve Gift Certificate"
LP - "Lost Password" .. Haven't tried
MC - Probably the old fastmail send message window.
MI - "Migrate IMAP Mailbox"
MS - "Search Messages" .. Unfortunately, this is not working It would be very useful
PE - "Personalities" .. Use Opera UI instead
PL - Settings for Personalities .. Use Opera UI instead
PM - "Purge folder" .. You can use this to archive, purge and remove duplicate messages from your mailboxes.
PY - "Add Funds"
RA - "Add Account" .. Use Oper UI instead
SG - *Signtures* .. Use Opera UI instead
SU - "Support Form"
TI - "Create support ticket"
TV - "Ticket details"
UA - "Import/Export contacts" .. Use Opera UI instead
VD - "Virtual Domains" .. Not sure if or how does this work