RFC 8438

IMAP Extension for STATUS=SIZE

📅 published August 2018, from ietf

Internet Engineering Task Force (IETF) 🎀 RFC 8438: IMAP Extension for STATUS=SIZE ✨

Okay bestie, so this is an IETF Standards Track doc 💅 from August 2018, written by Stephan Bosch of Dovecot Oy 🦋. It's an official IETF Proposed Standard-level product, approved by the IESG, and it doesn't obsolete or update any other RFCs 🌸. Sweet and simple!

Abstract ✨

Okay so this doc adds a new capability called "STATUS=SIZE" to IMAP 💖. The whole point is that you can get a mailbox's total storage size with ONE STATUS command, instead of fetching and adding up the size of every single message in it 🧚. Main character efficiency. 💅

Status of This Memo 🌈

This is an Internet Standards Track doc 💜. It's a product of the IETF, it reflects the consensus of the IETF community, got public review, and was approved by the IESG 👑. If you want more on Internet Standards, check Section 2 of RFC 7841 🦋.

Info about the current status, errata, and feedback is at https://www.rfc-editor.org/info/rfc8438 🌸.

Copyright Notice 🎀

Copyright (c) 2018 IETF Trust and the document authors. All rights reserved 💅. This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they were on the publication date, so read those carefully bestie, they explain your rights 📜. Any code pulled out of this doc has to include Simplified BSD License text (Section 4.e of the Trust Legal Provisions) and comes with no warranty 🫶.

Table of Contents 🧚

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
3.  STATUS Command and Response Extensions  . . . . . . . . . . .   3
4.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   5
5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1. Introduction 🦋

Okay so this doc extends IMAP [IMAP4rev1] with the new "STATUS=SIZE" capability 💖. Right now, if a client wants a mailbox's total size, it has to grab every message size one at a time using FETCH with the RFC822.SIZE data item 😭. Ew. STATUS=SIZE is the upgrade: it adds a new "SIZE" data item to STATUS, which gives the total size of all messages in the target mailbox, so you only need ONE STATUS command 🧚✨. When LIST-STATUS [LIST-STATUS] is also around, you can grab SIZE for a bunch of mailboxes at once with just one LIST command 🔥.

This is super useful for clients that don't cache the state of the message store, like most webmail clients 💻. Without this capability, those clients have to fetch every message size from the server whenever they need one mailbox's size 🥲. Picture a user who wants detailed quota usage for each mailbox to see which ones are hogging storage 👀. With that info they can see which mailboxes need a cleanup to lower their quota usage 🧹. The QUOTA capability [QUOTA] doesn't help here, because QUOTAROOT only reports STORAGE usage for a whole quota root, not for each mailbox inside it 💀.

2. Conventions Used in This Document 🌸

In the examples, "C:" marks lines sent by a client connected to a server, and "S:" marks lines sent by the server to the client 💅.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this doc are read as BCP 14 [KEYWORDS] [KEYWORDS2] ONLY when they're in all capitals like shown here 🎀. Lowercase is just normal English, bestie 🫶.

3. STATUS Command and Response Extensions 👑

This extension defines ONE new status data item for the STATUS command and response 💖:

SIZE 🌈

The total size of the mailbox in octets 📦. It doesn't have to be an exact value, but it MUST be equal to or greater than the sum of the RFC822.SIZE FETCH message data item [IMAP4rev1] of all messages in the mailbox 🧮. If QUOTA [QUOTA] is also supported, this value SHOULD be equal to the storage usage value used to enforce the STORAGE resource limit for this mailbox 💅. That way, the client can directly infer the quota usage 🧚.

Since a mailbox's total storage size can easily go over 4 GB 😳, clients MUST be able to receive 63-bit SIZE data item values 💪. The message size is capped at 63 bits instead of 64 to make implementations on various platforms (like Java) easier 🍓.

Example:

C: A01 STATUS frop (MESSAGES SIZE UIDNEXT)
S: * STATUS frop (MESSAGES 8 SIZE 44421 UIDNEXT 242344)
S: A01 OK STATUS completed

The same info can be gotten using the following commands, albeit less efficiently 🙈:

C: A02 SELECT "frop"
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * 8 EXISTS
S: * 1 RECENT
S: * OK [UNSEEN 7] First unseen.
S: * OK [UIDVALIDITY 1364851417] UIDs valid
S: * OK [UIDNEXT 242344] Predicted next UID
S: * OK [HIGHESTMODSEQ 3914] Highest
S: A02 OK [READ-WRITE] Select completed.
C: A03 FETCH 1:* (RFC822.SIZE)
S: * 1 FETCH (RFC822.SIZE 3224)
S: * 2 FETCH (RFC822.SIZE 1222)
S: * 3 FETCH (RFC822.SIZE 444)
S: * 4 FETCH (RFC822.SIZE 4516)
S: * 5 FETCH (RFC822.SIZE 544)
S: * 6 FETCH (RFC822.SIZE 922)
S: * 7 FETCH (RFC822.SIZE 31126)
S: * 8 FETCH (RFC822.SIZE 2423)
S: A03 OK Fetch completed.

When LIST-STATUS [LIST-STATUS] is also available, STATUS can be combined with LIST to be even more efficient 🔥. That means you can get the sizes of many mailboxes with just one LIST command 🧚.

Example:

C: A04 LIST "" % RETURN (STATUS (MESSAGES SIZE))
S: * LIST () "." "INBOX"
S: * STATUS "INBOX" (MESSAGES 17 SIZE 16234)
S: * LIST () "." "frop"
S: * STATUS "frop" (MESSAGES 8 SIZE 44421)
S: A04 OK List completed.

4. Formal Syntax 💜

This syntax spec augments the grammar in [IMAP4rev1] and [IMAP4-ABNF] 📐. It uses ABNF [ABNF] notation. Anything not defined here comes from [IMAP4rev1] and [IMAP4-ABNF] 🫶.

capability     =/ "STATUS=SIZE"

status-att     =/ "SIZE"

status-att-val =/ "SIZE" SP number64

number64       = 1*DIGIT
                 ; Unsigned 63-bit integer
                 ; (0 <= n <= 9,223,372,036,854,775,807)

5. Security Considerations 🔐

Okay, security time, and I'm being serious 🫢. There are no known additional security issues with this extension beyond the ones already described for the base protocol [IMAP4rev1] and the LIST-STATUS extension [LIST-STATUS] 🛡️. Nothing new to panic about, but don't skip the base protocol's own security notes either 💀.

6. IANA Considerations 🌈

IANA has added "STATUS=SIZE" to the "IMAP Capabilities" registry at <http://www.iana.org/assignments/imap-capabilities> 🦋.

7. Normative References 📚

[ABNF]     Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
           Specifications: ABNF", STD 68, RFC 5234,
           DOI 10.17487/RFC5234, January 2008,
           <https://www.rfc-editor.org/info/rfc5234>.

[IMAP4-ABNF]
           Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
           ABNF", RFC 4466, DOI 10.17487/RFC4466, April 2006,
           <https://www.rfc-editor.org/info/rfc4466>.

[IMAP4rev1]
           Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
           4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
           <https://www.rfc-editor.org/info/rfc3501>.

[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119,
           DOI 10.17487/RFC2119, March 1997,
           <https://www.rfc-editor.org/info/rfc2119>.

[KEYWORDS2]
           Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
           2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
           May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[LIST-STATUS]
           Melnikov, A. and T. Sirainen, "IMAP4 Extension for
           Returning STATUS Information in Extended LIST", RFC 5819,
           DOI 10.17487/RFC5819, March 2010,
           <https://www.rfc-editor.org/info/rfc5819>.

[QUOTA]    Myers, J., "IMAP4 QUOTA extension", RFC 2087,
           DOI 10.17487/RFC2087, January 1997,
           <https://www.rfc-editor.org/info/rfc2087>.

Acknowledgements 🫶

Huge thanks to Bron Gondwana, Alexey Melnikov, Stan Kalisch, and Michael Slusarz for reviews and suggestions 💖.

Author's Address 🦋

Stephan Bosch Dovecot Oy Lars Sonckin Kaari 12 Espoo 02600 Finland

Email: stephan.bosch@dovecot.fi 💌

📦 where this page comes from

ietf: rfc8438 2018-08
💖 girlified by claude-haiku-5-5 on 2026-10-18: a language model's rewrite of the original, under its terms