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187 lines
5.2 KiB
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<META NAME="generator" CONTENT="http://txt2tags.org">
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<TITLE>Good practices for imapsync</TITLE>
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</HEAD><BODY BGCOLOR="white" TEXT="black">
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<CENTER>
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<H1>Good practices for imapsync</H1>
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<FONT SIZE="4"><I>Gilles LAMIRAL gilles@lamiral.info</I></FONT><BR>
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<FONT SIZE="4">% $Id: GOOD_PRACTICES.t2t,v 1.10 2019/11/25 12:50:54 gilles Exp gilles $</FONT>
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</CENTER>
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<P></P>
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<HR NOSHADE SIZE=1>
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<P></P>
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<UL>
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<LI><A HREF="#toc1">Good practices for imapsync</A>
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<UL>
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<LI><A HREF="#toc2">Simple transfer</A>
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<LI><A HREF="#toc3">Exact backup</A>
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<LI><A HREF="#toc4">Restore</A>
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<LI><A HREF="#toc5">Presync</A>
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</UL>
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</UL>
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<P></P>
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<HR NOSHADE SIZE=1>
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<P></P>
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<A NAME="toc1"></A>
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<H1>Good practices for imapsync</H1>
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<P>
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You are not supposed to have read the TUTORIAL documentation but
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reading it should help to understand and master the following best practices.
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</P>
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<A NAME="toc2"></A>
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<H2>Simple transfer</H2>
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<P>
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By principle, imapsync does not change any single byte of messages,
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unless --regexmess or --addheader is used.
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Imapsync identifies messages with "Message-Id" and "Received" headers,
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so it ignores messages that lack those headers;
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most of the time it happens with the "Sent" folders.
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</P>
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<P>
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A way to sync those messages is to add option --addheader.
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Before appending a message on host2, and only when needed,
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--addheader option adds a Message-Id header like "Message-Id: <123456789@imapsync>"
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where 123456789 is the host1 folder message UID. Messages on host1 stay untouched.
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This way, multiples runs will not generate duplicates as long as UIDs stay
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the same on host1, which is the case for most imap servers.
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</P>
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<P>
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Unix:
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</P>
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<PRE>
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imapsync \
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--host1 imap.truc.org --user1 foo --password1 secret1 \
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--host2 imap.trac.org --user2 bar --password2 secret2 \
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--addheader
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</PRE>
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<P>
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Windows:
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</P>
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<PRE>
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imapsync ^
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--host1 imap.truc.org --user1 foo --password1 secret1 ^
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--host2 imap.trac.org --user2 bar --password2 secret2 ^
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--addheader
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</PRE>
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<A NAME="toc3"></A>
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<H2>Exact backup</H2>
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<P>
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Assertions for this example:
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</P>
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<UL>
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<LI>The target account at host2 is considered like inactive.
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<LI>Everything a user does on host1 will be synced, folders, messages, flags.
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<LI>Everything a user does on host2 will be erased by the sync.
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<P></P>
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Two options are good for an exact backup, --delete2 and --delete2folders.
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<P></P>
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<LI>--delete2: deletes messages in host2 that are not in host1 server.
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<LI>--delete2folders: deletes folders in host2 that are not in host1 server.
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<P></P>
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Unix:
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<PRE>
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imapsync \
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--host1 imap.truc.org --user1 foo --password1 secret1 \
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--host2 imap.trac.org --user2 bar --password2 secret2 \
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--delete2 --delete2folders
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</PRE>
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Windows:
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<PRE>
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imapsync ^
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--host1 imap.truc.org --user1 foo --password1 secret1 ^
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--host2 imap.trac.org --user2 bar --password2 secret2 ^
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--delete2 --delete2folders
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</PRE>
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</UL>
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<P>
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Have in mind
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</P>
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<UL>
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<LI>Doing backups without restoring at least one time to check the process
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is like pissing in a violin or throwing away your messages.
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<LI>Manual backups are useless because manually you will never have the ones you need
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to restore, they will always be out of date.
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<LI>Automatic backups are the way to go. They never forget to start. But they may fail.
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<LI>Automatic backups can fail. How? Hard disks get fully filled, they crash.
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Networks fail too.
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<LI>Monitor the backups.
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<LI>Remember you have backups.
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<LI>Document the restoring process or consider the backup is a just a lost trash.
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<LI>Think twice at least before running any restoring command.
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Restoring is dangerous.
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</UL>
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<A NAME="toc4"></A>
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<H2>Restore</H2>
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<P>
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Restoring is not the exact reverse of backupping
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since between a backup and a mistake, the context has changed,
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some things went wrong but not all, for examples new messages arrived.
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So synchronize an active account identical from a backup might not be the best idea.
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</P>
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<P>
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The context can be a crash or equivalent like when a
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not friendly admin or service closed definitevely access to your messages.
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Even in that case an exact restore, with --delete2 --delete2folders, should not be ok,
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just because new messages arrive in INBOX all the time.
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</P>
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<A NAME="toc5"></A>
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<H2>Presync</H2>
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<P>
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Presync is like a backup except deleting folders on host2 that
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are not on host1 is not always wanted. Presync means a new
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different imap server will host messages and folders.
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Often this new imap server has predefined folders that
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should be kept for proper use, so I suggest to not use
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option --delete2folders.
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</P>
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<P>
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Unix:
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</P>
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<PRE>
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imapsync \
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--host1 imap.truc.org --user1 foo --password1 secret1 \
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--host2 imap.trac.org --user2 bar --password2 secret2 \
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--delete2
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</PRE>
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<P>
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Windows:
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</P>
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<PRE>
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imapsync ^
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--host1 imap.truc.org --user1 foo --password1 secret1 ^
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--host2 imap.trac.org --user2 bar --password2 secret2 ^
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--delete2
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</PRE>
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