Mailpiler integration for archived email in Mail client

Is your feature request related to a problem? Please describe.

• https://github.com/nextcloud/mail/issues/22#issuecomment-913746984

@JPustkuchen it would indeed be great if you can open a separate issue for that so it does not get lost, thank you! :)

• https://github.com/nextcloud/mail/issues/22#issuecomment-1285205178

Seems this excellent idea was not added to a new issue, so doing that.
piler aka Mailpiler, is a PHP-based Open Source Email Archiving service for enterprises.
Bitbucket repo
List of features and PHP coding make it a very appealing companion to Nextcloud Mail client! Biggest headache with such a project is not having it integrated into a mail client.

Cheers and Happy Holidays.

Built-in SMTP server
STARTTLS support
Virus checking (using clamav)
Exclusion (formerly: archiving) rules
Retention rules
Attachment deduplication
Zlib compression
AES-256 encryption (formerly: Blowfish)
Digital signing and verification

Searching

Simple search
Advanced search
Save/load search criteria
Tagging emails
Adding notes to emails
View/export/restore of archived emails

Web interface

Access with a browser
AD/LDAP authentication
Single Sign-on
Google OAuth
IMAP authentication
POP3 authentication
2 factor authentication (2FA)
Custom authentication hooks
Access control
i18n

Monitoring / Audit

Logging of events
Search the audit logs
Legal hold
Status info/chart

Import / Export

Export to EML format
Import from PST (using readpst), EML and mailbox format
Import from POP3/IMAP account

S3 object storage
Full Text Search
Rest API

Describe the solution you'd like

Mailpiler integration for Mail Client, as linked from previous thread

Describe alternatives you've considered

Running Mailpiler by itself

Additional context

No response

No files, tests, or entry points are named. Start by reviewing Mailpiler's documented REST API and the Mail client's existing integration architecture; define the supported archive, search, view, export, and restore flows before implementation, with done meaning those flows work and are tested.