Email Archiving Principles

Glossary

mailbox … user's mail storage area on a mail server, keeps messages in folders, limited size.
mail client … (Thunderbird, Outlook, etc.) accesses mailbox via IMAP protocol (makes local copy of the mailbox on user’s computer).
webmail client … accesses a mailbox via web browser
email archiving … systematic approach to saving and protecting the data contained in e-mail messages so it can be accessed quickly at a later date
local folders… set of mail folders located on the computer where mail client is installed and running

Users must be aware of the limited size of their institutional mailbox.
Regular maintaining of the mailbox is recommended (see below for details and hints).
Users should make regular backup of their local archive folder

There are several ways to achieve this:

unnecessary messages wiping (after deleting empty the recycle bin folder)
bigger attachments detaching (sort emails by size and deliberately remove the biggest attachments)
move messages to your computer mail folder (archiving to local archive) and make backup of your archive regularly then

You can archive messages by moving them to Local folders in your mail client (Thunderbird)
Make immediately a fresh copy of the local archive to a different storage media (external disc, etc.)
Be aware that your local archive is on your computer so its content is not accessible via webmail

classify messages by durability (assign a folder for temporary messages, mark, tag, etc.)
make “preliminary archive” folder inside of server's mailbox, continuously process messages movement
move spasmodically (regularly or on demand) messages from the pre-archive to the local archive folders
this significantly reduces the need to copy the local archive to the external media
the local folders copy on the external disc could be connected and used off-line, kept and distributed