Very roughly translated from the Opera Fansite with permission — Could use some polishing up.
Opera\Mail\Accounts.ini stores information about Mail accounts
[Accounts] AccountX = Account numbers and IDs. The number indicates, which of the accounts specified below is used. Default Mail account = Specifies the standard account for Mails Default News account = Specifies the standard account for News Active account Category = The active account category Active account = Specifies the active account Count = Number of active accounts Next Available ID = next account ID not assigned yet. The ID of a deleted account is not reused by M2. [Account1] Temporary = If this is 1 the account will be deleted when Opera exits Incoming Protocol = Minutes for incoming (POP, IMAP, NNTP, IRC) Outgoing Protocol = Minutes for exit (smtp, IMAP) Incoming Port = port for incoming servers Outgoing Port = port for outgoing servers Secure Connection in = Safe connection for incoming servers to use Secure Connection Out = Safe connection for outgoing servers to use Secure Authentication = (0=no,1=yes) Incoming Authentication Method = Authenticationmethod for incoming server (31=Auto, 10=AUTH CRAM MDS, 5=AUTH-LOGIN, 1=only text, 0=none) Outgoing Authentication Method = Authenticationmethod for output servers Incoming Timeout = Seconds after which an idle connection to the incoming server will be dropped Outgoing Timeout = Seconds after which an idle connection to the outgoing server will be dropped Download Bodies = Download Message bodies (0=no,1=yes) Keep Bodies = store local copy of the message (0=no,1=yes) Leave on server = Leave mails on server Queue Outgoing = Queue outgoing messages Send Queued after checks = only send after receive Mark Read If Seen = as read mark if already downloaded Sound Enabled = Sound signal Manual check Enabled = include account when manual checking for mail Account name = Account name Category = Account category Incoming server name = incoming server Incoming username = User name for incoming servers Incoming passwords = Password for incoming servers Outgoing server name = Output server Outgoing username = User name for outgoing servers Outgoing passwords = Password for outgoing servers Charset = Standard character set for outgoing Mails Force Charset = force Character set Allow 8-bit headers = Permit 8-bit header data (may break old clients) Allow 8-bit transfer = Mails with 8-bits transfer Preferred Mail Body mode = 0=prefer Text, 1=prefer HTML. Currently ignored, use View - Display in a mail view instead. Real Name = Name of the user Email = Mailadress of the user Organization = Organization Replyto = Reply-to address Fqdn = Fully Qualified Domain Name (rear part of the Message ID). Should be automatically filled in. Reply = Introduction line for replies Forward = Introduction line for Forwards Followup = Introduction line for Followups (newsgroup replies) Line length = Message Line length, used for wrapping. Has no meaning in a client which understands format=flowed. Remove Signature on Reply = Remove Signature when replying to a message Max QuoteDepth on Reply = only X levels will be quoted on reply Max QuoteDepth on QuickReply = only X levels will be quoted on QuickReply Signature file = File with signature. Usually signatureX.txt in the mail directory, with X being the account number. Personalization = Inserts the indicated text in the Message ID before @. Sound file = This sound file plays if new mail for this account is received Incoming log file = Log file for incoming messages Outgoing log file = Log file for outgoing messages IMAP folder collection path = Path to the files of the IMAP of profiles IMAP sent mail folders path = Path to "sent" folder on the IMAP server Auto CC = Add this address automatically as CC Auto BCC = Add this address automatically as BCC Polling Interval = Check for new mail every X seconds Add Contact When Sending = Add contact when sending a message Display header flag = Bit 0 - Account (or of, like it for the moment one calls), bits 1 - Identity and signature., bit 2 - priority, bit 3 - tons, bit 4 - CC, bit 5 - Bcc, bit 6 - newsgroup, bit 7 - Followup tons, bit 8 - organization, bit 9 - Subject, bit 10 - Attachments, bit 11 - Reply to Incoming options file = Options for incoming messages Outgoing options file = Options for outgoing messages **Not Yet Implemented** Max Download Size = from Mails those are larger than indicated (in KB) only header data will be downloaded Purge Age = Delete Mails after X days automatically (only IMAP) Purge Size = Delte mails automatically , if the database achieves a certain size Download Attachments = Attachments download Xface = String with your X-Face. M2 will currently send these, but cannot display them yet.
Warning: this file is not meant to be edited by hand. You may lose all your mail indexing if you make a mistake.
[Indexer] NEXT Contact ID = Next available ID for an active contact (initial value: 100000000) NEXT folder ID = Next available ID for a file (initial value: 200000000) NEXT search ID = Next available ID for a search (initial value: 300000000) NEXT newsgroup ID = Next available ID for newsgroup (initial value: 400000000) NEXT Thread ID = Next available ID for an active Thread (initial value: 600000000) NEXT IMAP ID = Next available ID for a IMAP file (initial value: 700000000) NEXT new feed ID = Next available ID for a new feed (initial value: 1200000000) Index Count = Number of indexes Reindexing Message = Display the Index dialog on the next start Indexer version = Indexer version. If these two lines are missing Opera will index all messages again on restart [Categories] Category 0 open = All messages in the Hotlist opened indicate (0=closed, 2=open) Category 0 unread = Into all messages are unread messages (0=no, 1=yes) Category 1 open = Mailing lists in the Hotlist opened indicate (0=closed, 2=open) Category 1 unread = Mailing lists are unread message (0=no, 1=yes) Category 2 open = Active contacts in the Hotlist opened indicate (0=closed, 2=open) Category 2 unread = Active contacts are unread message (0=no, 1=yes) Category 3 open = active Threads in the Hotlist opened indicates (0=closed, 2=open) Category 3 unread = active Threads is unread message (0=no, 1=yes) Category 4 open = Categories in the Hotlist opened indicate (0=closed, 2=open) Category 4 unread = Categories are unread message (0=no, 1=yes) Category 5 open = Appendices in the Hotlist geÃoefnet indicate (0=closed, 2=open) Category 5 unread = Appendices are unread message (0=no, 1=yes) Category 6 open = Searches in the Hotlist opened indicate (0=closed, 2=open) Category 6 unread = Searches are unread message (0=no, 1=yes) Category 7 open = Newsgroup in the Hotlist opened indicate (0=closed, 2=open) (no longer used) Category 7 unread = Newsgroup are unread message (0=no, 1=yes) (no longer used) Category 8 open = own files in the Hotlist opened indicate (0=closed, 2=open) Category 8 unread = own files are unread message (0=no, 1=yes) Category 9 open = IMAP listings in the Hotlist opened indicate (0=closed, 2=open) (no longer used) Category 9 unread = IMAP listings are unread message (0=no, 1=yes) (no longer used) [Spam filter] Start Score = Initial value for internal Spam filter. The larger, the less mails are marked are Spam. [index X] Name = Name of the file ID = ID of the file Parent ID = ID of the containing file Type = Kind of the file (0=Mailinglist, 1=Search, 2=Mail, 3=Newsgroup, 4=IMAP, 5=Newsfeed) Visible = Files indicate (0=no, 1=yes) Account ID = Only indicate Mails of an account Model type = Indicator kind (0=plain, 1=threaded) Model Age = Only Mails from certain period indicate (0=Today 1=Week, 2=Month, 3=3 months, 4=year, 5=always) Model flags = determines which message be indicated. Around several options to activate their values add (1=read, 2=trash, 4=spam, 8=mailinglists, 16=newsgroups, ** 32 =???**, 64=Newsfeeds) Sort type = sort according to X (0=unsorted, 1=status, 2=sender, 3=subject, 4=date, 5=size, 6=onhang, 7=Category) Sort Ascending = Sortorder (1=decreasing, 0=increasing) Hide from Other = Mails in this view aren't shown in other views (0=no, 1=yes) Auto filter = learning filter enabled (0=no, 1=yes) Mark match As Read = Messages marked as read automatically (0=no, 1=yes) Inherit filters = inhert filters from the parent filter (0=no, 1=yes) Update frequencies = all X seconds update Load update time = Time of the last actualization in seconds starting from 01.01.1970 00:00 GMT File = Index file for this file Search text = text we are searching for Search Field = (1=Name, 2=Subject, 3=all headers, 4=full message, 6=From-Header, 7=To-Header, 8=CC, 9=Reply-To, 10=Newsgroup) Search Current Message = filter existing messages (0=no, 1=yes) Search start Date = Point of starting time in seconds starting from 01.01.1970 00:00 GMT Search end to Date = End-time in seconds starting from 01.01.1970 00:00 GMT Search option = (0=entire phrase, 1=each word, 2=RegExp, 3=doesn't contain) Search operator = for combinations of filters, only meaningfull starting from "search operator 2" (0=or, 1=and) Search Count = Number of search statements Search text 2 = search text Search Field 2 = search Field Search option 2 = search option Search operator 2 = Options for second search word (search COUNT must be larger than 1) Search is Regexp = currently unused