Per‑Client Time‑Zone Conversion for Dovecot IMAP Dates?

Question

Background
Dovecot parses the RFC‑5322 Date: header of each message and stores the resulting timestamp internally in UTC.  The original header is preserved unchanged.
When a client issues an IMAP SEARCH SINCE/BEFORE/ON command, the server interprets the date arguments relative to its configured local time zone.  This can lead to off‑by‑one‑day results for clients operating in different zones, and there is no built‑in mechanism for the server to return dates adjusted to a client’s preferred zone.
Unresolved Decision
Should Dovecot add optional per‑client timezone conversion for message dates in IMAP responses and SEARCH handling, or continue to rely on client‑side conversion?
What configuration changes would be required to enable such a feature, and how would it affect backward compatibility and performance?
Can Dovecot support optional per‑client timezone conversion for message dates in IMAP responses?

Tasadduq Burney · Answer

Answer to the Question
Short answer: No.  Dovecot 3.x does not provide an out‑of‑the‑box per‑client time‑zone conversion for IMAP SEARCH or FETCH responses.  The server converts all RFC‑5322 Date: headers to UTC on storage and, when a client issues a date‑based search, it interprets the supplied date string using the server’s configured local time zone (or mailbox_timezone if set).  Clients must perform any client‑side conversion.
Why the Feature Isn’t Present

The IMAP protocol itself has no standard keyword for a client’s preferred time zone.
Adding a non‑standard extension (e.g., X-CLIENT-TZ) would break strict‑mode clients that reject unknown keywords.
Server‑side conversion would add per‑message CPU work during FETCH and SEARCH, potentially impacting performance on busy servers.

What You Can Do Now

Align the server’s time zone.  If all clients are in a single region, set mailbox_timezone = Europe/Paris (or your zone) in 10-mail.conf so that the server’s interpretation matches the clients.
Use client‑side conversion.  Most modern IMAP clients (Thunderbird, Outlook, mobile apps) expose a time‑zone setting that automatically adjusts dates in the UI.
Consider a custom wrapper.  If you must keep the server in UTC, write a small proxy that injects a X-CLIENT-TZ header and rewrites FETCH responses.  This is non‑standard and should be tested against all clients you support.

Potential Future Implementation (Hypothetical)
If Dovecot were to add per‑client conversion, a new configuration directive such as per_client_timezone = yes would be required, along with support for an IMAP keyword to carry the client’s zone.  Backward compatibility could be preserved by treating unknown keywords as no‑ops for legacy clients, but performance would need to be benchmarked because each FETCH would involve a time‑zone lookup.
Missing Diagnostic Detail
Which Dovecot version are you running?  The feature set can differ between 3.0, 3.2, and any custom patches you may have applied.

Per‑Client Time‑Zone Conversion for Dovecot IMAP Dates?

Background

Unresolved Decision

1 answer

Answer to the Question

Why the Feature Isn’t Present

What You Can Do Now

Potential Future Implementation (Hypothetical)

Missing Diagnostic Detail

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