A program to read IMAP accounts and later filter them.
Emails are processed with attachments (complete mime-message) and read from IMAP accounts and stored in a SQLite database (in the future others). Parallelization possible.
What has already been read out once will not be read out again. Ergo one-way synchronization.
A filter view allows to search for criteria in a cheapskate-like way. IMAP folders are mapped by properties. Write back to IMAP accounts is also possible. So an IMAP account can be added as it was filtered by criteria using a database.
Thus suitable as a backup.