**Feature Request: Preserve IMAP \Seen flag on fetch by using BODY.PEEK[]**

[chc-pr]

Is your feature request related to a problem?

No, at present this missing feature is a hard pass for implementation. I have tried retesting a few times over a few years but keep hitting this wall.

Describe the solution you'd like

Proposed behaviour

• All message body fetches during sync should use BODY.PEEK[] (or the MailKit PEEK-equivalent) so that the \Seen flag on the IMAP server is never altered by the archiver
• The archiver should record the \Seen flag state at the time of fetch (already read or unread) and store it in the archive metadata, so the archive accurately reflects the read status at time of archiving
• The archiver should never write any flag changes back to the IMAP server under any circumstances during normal sync operation

Additional context

Describe the feature

When Mail-Archiver fetches messages from an IMAP server, it should use BODY.PEEK[] rather than BODY[] to retrieve message content. This is a standard IMAP mechanism (defined in RFC 3501) that retrieves the full message body without triggering the server to set the \Seen flag as a side effect.

Currently, fetching messages via BODY[] (or the MailKit equivalent GetMessageAsync) causes most IMAP servers to automatically mark those messages as read. This is destructive behaviour for an archiver, which should be entirely non-mutating toward the source mailbox.

Why this matters

An email archiver's role is to observe and preserve — not to alter the state of the source mailbox in any way. Users rely on the unread/read status of their emails to manage their workflow. If archiving silently marks unread emails as read on the server, this:

• Causes users to miss emails they have not yet acted on
• Makes the archiver unsafe to run against production mailboxes
• Breaks the fundamental principle that archiving should be non-destructive

This is a well-known IMAP pitfall. The fix is: replace any BODY[] fetch calls with BODY.PEEK[], or use MailKit's GetStream/fetch API in a way that does not implicitly set \Seen.

Further Additional context

The MailKit library used by Mail-Archiver does support PEEK-style fetching. The stack trace visible in issue #236 confirms that MailKit.Net.Imap.ImapFolder.GetMessageAsync(UniqueId uid...) is the current fetch method — this method does set \Seen on most servers. The solution is to use the lower-level MailKit fetch API with BodyPartBasic and PEEK semantics instead.

This change would make Mail-Archiver suitable for users migrating from commercial archivers such as Mailstore, where non-destructive IMAP fetching is a baseline expectation.

Happy to assist with testing against a live IMAP account if that would be useful during development.

If you have got this far, thank you for taking the time to review this request.