Capture the pre-migration snapshot from 0.15.x, and stop claiming counts match when none were compared

Found by running preflight against a real Stalwart 0.15.5 in a VM. Two
defects, the second worse than the first.

1. AccountSnapshot could not read the version this tool migrates FROM.
   0.15.5 advertises no urn:stalwart:jmap capability and POST /api returns
   404 - the JMAP management API and x:Account are 0.16 features. 0.15.x
   exposes a REST API at GET /api/principal instead. So preflight's
   account-snapshot check warned and moved on, and every run against a real
   source instance had no "before" data at all.

   AccountSnapshot now dispatches on the capability the session document
   advertises - a positive signal, not an inference from a failed call -
   and internal/stalwartapi/principal.go implements the 0.15.x REST path,
   including its 1-based page/limit pagination so an install larger than
   one page isn't silently truncated.

2. With no "before" counts, the content-integrity comparison iterated an
   empty map, checked nothing, and reported "all message counts match".
   That is the strongest claim this tool makes - ARCHITECTURE 4.7 calls it
   the actual no-data-loss guarantee - made vacuously, and it would have
   passed on a migration that lost every message.

   The comparison now derives its account set from whatever the source
   could report, verifies every account and domain survived either way, and
   carries MessageCountsCompared so the report says plainly "MESSAGE COUNTS
   NOT COMPARED ... no-data-loss is NOT verified here" rather than implying
   otherwise.

What can and cannot be checked across the 0.15/0.16 boundary, now that a
real server has answered: 0.15.x has no per-mailbox message count at any
endpoint, and the impersonation login 0.16 offers returns 401 there, so
before/after message counts are impossible for the boundary migration this
tool exists for. Both versions do report per-account used quota (usedQuota
in 0.15's REST list, usedDiskQuota on 0.16's x:Account), so that is
captured on both sides. It is recorded and reported, not asserted on:
4.5 notes the 0.16 migration resets quotas to zero pending recalculation,
so comparing those bytes across the boundary would be a false alarm
generator.

Test servers across preflight, validate and stalwartapi now advertise
urn:stalwart:jmap, since they stand in for 0.16 instances and that
capability is what says so.

Verified end to end against the smoke VM: all nine preflight checks pass,
and the checkpoint records 2 accounts, 1 domain and per-account used quota
where it previously recorded nothing.

internal/stalwartapi/client.go

@@ -63,6 +63,12 @@ type Snapshot struct {
 	AccountCount  int
 	Domains       []string
 	MailboxCounts map[string][]MailboxCount // account email -> its mailboxes
+	// UsedQuota is each account's used storage in bytes. Unlike
+	// MailboxCounts it is available from both API generations - 0.15.x's
+	// REST principal list and 0.16's x:Account both report it - which
+	// makes it the only per-account content measure that can be compared
+	// across the 0.15/0.16 boundary. See principal.go.
+	UsedQuota map[string]int64
 	// MailboxErrors records, per account email, why that account's mailbox
 	// counts couldn't be captured (e.g. impersonation not permitted for
 	// that account). A non-empty entry here means MailboxCounts has no

internal/stalwartapi/mailbox.go

@@ -20,6 +20,10 @@ import (
 type jmapSession struct {
 	APIURL          string            `json:"apiUrl"`
 	PrimaryAccounts map[string]string `json:"primaryAccounts"`
+	// Capabilities is what the instance says it supports. Its contents
+	// decide which management API this client speaks - see
+	// stalwartManagementCapability.
+	Capabilities map[string]json.RawMessage `json:"capabilities"`
 }
 
 const jmapMailCapability = "urn:ietf:params:jmap:mail"

internal/stalwartapi/management.go

@@ -104,6 +104,10 @@ type account struct {
 	ID       string `json:"id"`
 	Name     string `json:"name"`
 	DomainID string `json:"domainId"`
+	// UsedDiskQuota is 0.16's name for what 0.15's REST API calls
+	// usedQuota - the same per-account byte count, which is what makes a
+	// cross-boundary content comparison possible at all.
+	UsedDiskQuota int64 `json:"usedDiskQuota"`
 }
 
 // AccountSnapshot enumerates every account on the instance via Stalwart's
@@ -124,6 +128,22 @@ type account struct {
 // exactly what's missing rather than silently treating an unreachable
 // account's mailboxes as having zero messages.
 func (c *Client) AccountSnapshot(ctx context.Context) (*Snapshot, error) {
+	isJMAP, err := c.hasJMAPManagement(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("stalwartapi: discover which management API this instance speaks: %w", err)
+	}
+	if !isJMAP {
+		// No urn:stalwart:jmap: this is a 0.15.x instance, whose
+		// management API is REST. Confirmed against a live 0.15.5 server -
+		// see principal.go.
+		return c.principalSnapshotREST(ctx)
+	}
+	return c.accountSnapshotJMAP(ctx)
+}
+
+// accountSnapshotJMAP is the 0.16+ path, via Stalwart's JMAP management
+// objects.
+func (c *Client) accountSnapshotJMAP(ctx context.Context) (*Snapshot, error) {
 	ids, err := c.AccountIDs(ctx)
 	if err != nil {
 		return nil, err
@@ -133,7 +153,7 @@ func (c *Client) AccountSnapshot(ctx context.Context) (*Snapshot, error) {
 	}
 
 	getResp, err := c.call(ctx, managementCapabilities, []any{
-		[]any{"x:Account/get", map[string]any{"ids": ids, "properties": []string{"id", "name", "domainId"}}, "g"},
+		[]any{"x:Account/get", map[string]any{"ids": ids, "properties": []string{"id", "name", "domainId", "usedDiskQuota"}}, "g"},
 	})
 	if err != nil {
 		return nil, fmt.Errorf("stalwartapi: Account/get: %w", err)
@@ -169,11 +189,19 @@ func (c *Client) AccountSnapshot(ctx context.Context) (*Snapshot, error) {
 	}
 	sort.Strings(domains)
 
+	usedQuota := make(map[string]int64, len(accounts))
+	for _, a := range accounts {
+		if a.Name != "" {
+			usedQuota[a.Name] = a.UsedDiskQuota
+		}
+	}
+
 	return &Snapshot{
 		AccountCount:  len(accounts),
 		Domains:       domains,
 		MailboxCounts: mailboxCounts,
 		MailboxErrors: mailboxErrors,
+		UsedQuota:     usedQuota,
 	}, nil
 }
 

internal/stalwartapi/management_test.go

@@ -12,6 +12,21 @@ import (
 	"testing"
 )
 
+// serveJMAPSession answers session discovery for a server standing in for
+// a 0.16+ instance: what marks it as one is the urn:stalwart:jmap
+// capability, which is exactly what AccountSnapshot dispatches on. Returns
+// true if it handled the request.
+func serveJMAPSession(w http.ResponseWriter, r *http.Request, apiURL string) bool {
+	if r.Method != http.MethodGet || r.URL.Path != "/.well-known/jmap" {
+		return false
+	}
+	json.NewEncoder(w).Encode(map[string]any{
+		"apiUrl":       apiURL,
+		"capabilities": map[string]any{"urn:ietf:params:jmap:core": map[string]any{}, "urn:stalwart:jmap": map[string]any{}},
+	})
+	return true
+}
+
 // jmapEnvelope mirrors the wire shape this package's call() parses: a
 // top-level {"methodResponses": [...]} object where each entry is a
 // [name, args, callId] triple (RFC 8620 §3.2).
@@ -35,6 +50,12 @@ func accountManagementAndMailboxServer(t *testing.T, mailboxesFor map[string][]m
 
 		if r.Method == http.MethodGet && r.URL.Path == "/.well-known/jmap" {
 			user, _, _ := r.BasicAuth()
+			if !strings.Contains(user, "%") {
+				// The client's own session request, used to decide which
+				// management API this instance speaks.
+				serveJMAPSession(w, r, apiURL)
+				return
+			}
 			target := strings.SplitN(user, "%", 2)[0]
 			if _, ok := mailboxesFor[target]; !ok {
 				w.WriteHeader(http.StatusForbidden)
@@ -140,6 +161,9 @@ func TestAccountSnapshotRecordsPerAccountMailboxFailureWithoutFailingOverall(t *
 
 func TestAccountSnapshotEmptyInstance(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if serveJMAPSession(w, r, "/api") {
+			return
+		}
 		json.NewEncoder(w).Encode(jmapEnvelope{MethodResponses: []any{
 			[]any{"x:Account/query", map[string]any{"ids": []string{}}, "q"},
 		}})
@@ -158,6 +182,9 @@ func TestAccountSnapshotEmptyInstance(t *testing.T) {
 
 func TestAccountSnapshotPropagatesJMAPError(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if serveJMAPSession(w, r, "/api") {
+			return
+		}
 		json.NewEncoder(w).Encode(jmapEnvelope{MethodResponses: []any{
 			[]any{"error", map[string]any{"type": "forbidden"}, "q"},
 		}})
@@ -191,6 +218,9 @@ func TestAccountSnapshotSendsBasicAuth(t *testing.T) {
 		if !ok || user != "admin" || pass != "hunter2" {
 			t.Errorf("BasicAuth = (%s, %s, %v), want (admin, hunter2, true)", user, pass, ok)
 		}
+		if serveJMAPSession(w, r, "/api") {
+			return
+		}
 		json.NewEncoder(w).Encode(jmapEnvelope{MethodResponses: []any{
 			[]any{"x:Account/query", map[string]any{"ids": []string{}}, "q"},
 		}})

internal/stalwartapi/principal.go

@@ -0,0 +1,197 @@
+// SPDX-FileCopyrightText: 2026 LINUXexpert-org
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package stalwartapi
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"sort"
+	"strings"
+)
+
+// Stalwart 0.15.x - the version this tool migrates *from* - has no
+// urn:stalwart:jmap capability and no JMAP management endpoint: POST /api
+// returns 404 there. Its management API is REST, at GET /api/principal,
+// and that is the only way to enumerate the pre-migration directory.
+//
+// This was found by running preflight against a real 0.15.5 instance, not
+// from documentation: the published schema reference documents 0.16, and
+// following it alone produced a tool that could not read the source
+// version it exists to migrate. The shapes below were confirmed against
+// that live server.
+//
+//	GET /api/principal?types=individual&limit=100&page=1
+//	{"data":{"items":[{"id":4,"type":"individual","name":"alice",
+//	                   "emails":["[email protected]"],"usedQuota":9207}],
+//	         "total":3}}
+//
+// Two limits of the 0.15 side are worth stating plainly, because they
+// decide what the post-migration comparison can actually assert:
+//
+//   - There is no per-mailbox message count anywhere in this API, and the
+//     impersonation mechanism 0.16 offers (the `<target>%<impersonator>`
+//     composite login MailboxSnapshot uses) returns 401 on 0.15.5. So a
+//     pre-migration snapshot cannot carry message counts, and a
+//     before/after comparison of them is impossible for the boundary
+//     migration this tool is built for.
+//   - What both versions do expose per account is used quota in bytes
+//     (`usedQuota` here, `usedDiskQuota` on 0.16's x:Account). That is a
+//     real content measure - it moves when mail is lost - so it is what
+//     the integrity comparison uses across the boundary.
+const restPrincipalPageSize = 100
+
+// stalwartManagementCapability is advertised by instances whose management
+// API is the JMAP one (0.16+). Its absence is what distinguishes a 0.15.x
+// instance, and is a positive signal rather than an inference from a failed
+// call.
+const stalwartManagementCapability = "urn:stalwart:jmap"
+
+// hasJMAPManagement reports whether this instance speaks the 0.16+ JMAP
+// management API, by reading the capability list from its session
+// document. It deliberately does its own request rather than reusing
+// fetchSession: that helper also requires an apiUrl and a mail account,
+// which are needed for impersonated mailbox reads but have nothing to do
+// with which management API to use - failing dispatch over a missing
+// apiUrl would misroute an instance that is perfectly readable.
+func (c *Client) hasJMAPManagement(ctx context.Context) (bool, error) {
+	endpoint := strings.TrimRight(c.BaseURL, "/") + "/.well-known/jmap"
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return false, err
+	}
+	req.SetBasicAuth(c.Username, c.Password)
+	resp, err := c.httpClient().Do(req)
+	if err != nil {
+		return false, fmt.Errorf("stalwartapi: reach %s: %w", endpoint, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return false, fmt.Errorf("stalwartapi: session discovery at %s returned %s", endpoint, resp.Status)
+	}
+	var session struct {
+		Capabilities map[string]json.RawMessage `json:"capabilities"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&session); err != nil {
+		return false, fmt.Errorf("stalwartapi: parse session document from %s: %w", endpoint, err)
+	}
+	_, ok := session.Capabilities[stalwartManagementCapability]
+	return ok, nil
+}
+
+type restPrincipal struct {
+	ID        int      `json:"id"`
+	Type      string   `json:"type"`
+	Name      string   `json:"name"`
+	Emails    []string `json:"emails"`
+	UsedQuota int64    `json:"usedQuota"`
+}
+
+type restPrincipalPage struct {
+	Data struct {
+		Items []restPrincipal `json:"items"`
+		Total int             `json:"total"`
+	} `json:"data"`
+}
+
+// restPrincipals fetches every principal of the given type, following the
+// API's 1-based page/limit pagination rather than assuming one request
+// returns everything - an install with more accounts than the page size
+// would otherwise be silently truncated, and a truncated "before" snapshot
+// would make the post-migration comparison claim more than it checked.
+func (c *Client) restPrincipals(ctx context.Context, principalType string) ([]restPrincipal, error) {
+	var all []restPrincipal
+	for page := 1; ; page++ {
+		q := url.Values{}
+		if principalType != "" {
+			q.Set("types", principalType)
+		}
+		q.Set("limit", fmt.Sprint(restPrincipalPageSize))
+		q.Set("page", fmt.Sprint(page))
+		endpoint := strings.TrimRight(c.BaseURL, "/") + "/api/principal?" + q.Encode()
+
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+		if err != nil {
+			return nil, err
+		}
+		req.SetBasicAuth(c.Username, c.Password)
+		resp, err := c.httpClient().Do(req)
+		if err != nil {
+			return nil, fmt.Errorf("stalwartapi: list principals: %w", err)
+		}
+		body, readErr := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+		resp.Body.Close()
+		if resp.StatusCode != http.StatusOK {
+			return nil, fmt.Errorf("stalwartapi: GET %s returned %s: %s", endpoint, resp.Status, strings.TrimSpace(string(body)))
+		}
+		if readErr != nil {
+			return nil, fmt.Errorf("stalwartapi: read principal list: %w", readErr)
+		}
+		var parsed restPrincipalPage
+		if err := json.Unmarshal(body, &parsed); err != nil {
+			return nil, fmt.Errorf("stalwartapi: parse principal list: %w", err)
+		}
+		all = append(all, parsed.Data.Items...)
+		if len(parsed.Data.Items) == 0 || len(all) >= parsed.Data.Total {
+			return all, nil
+		}
+	}
+}
+
+// principalSnapshotREST builds a Snapshot from the 0.15.x REST management
+// API. MailboxCounts is deliberately left empty: see this file's opening
+// comment for why counts cannot be obtained from a 0.15 instance at all.
+func (c *Client) principalSnapshotREST(ctx context.Context) (*Snapshot, error) {
+	individuals, err := c.restPrincipals(ctx, "individual")
+	if err != nil {
+		return nil, err
+	}
+	domainPrincipals, err := c.restPrincipals(ctx, "domain")
+	if err != nil {
+		return nil, err
+	}
+
+	snap := &Snapshot{
+		AccountCount: len(individuals),
+		UsedQuota:    make(map[string]int64, len(individuals)),
+	}
+	for _, p := range individuals {
+		snap.UsedQuota[accountKey(p)] = p.UsedQuota
+	}
+
+	domainSet := map[string]bool{}
+	for _, d := range domainPrincipals {
+		if d.Name != "" {
+			domainSet[d.Name] = true
+		}
+	}
+	// Fall back to the domains implied by account addresses if the
+	// instance has no explicit domain principals.
+	for _, p := range individuals {
+		for _, email := range p.Emails {
+			if at := strings.LastIndex(email, "@"); at >= 0 && at+1 < len(email) {
+				domainSet[email[at+1:]] = true
+			}
+		}
+	}
+	for d := range domainSet {
+		snap.Domains = append(snap.Domains, d)
+	}
+	sort.Strings(snap.Domains)
+	return snap, nil
+}
+
+// accountKey identifies an account the same way both API generations can:
+// by its primary email address where it has one, falling back to the bare
+// login name. The v0.16 migration rewrites bare names into addresses, which
+// is exactly why the comparison side matches on local part as well.
+func accountKey(p restPrincipal) string {
+	if len(p.Emails) > 0 && p.Emails[0] != "" {
+		return p.Emails[0]
+	}
+	return p.Name
+}

internal/stalwartapi/principal_test.go

@@ -0,0 +1,183 @@
+// SPDX-FileCopyrightText: 2026 LINUXexpert-org
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package stalwartapi
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+// stalwart015Server stands in for a 0.15.x instance: no urn:stalwart:jmap
+// capability, POST /api is 404, and the management API is REST at
+// /api/principal with 1-based page/limit paging. Every shape here was
+// confirmed against a live 0.15.5 server.
+func stalwart015Server(t *testing.T, individuals, domains []map[string]any) (*httptest.Server, *[]string) {
+	t.Helper()
+	var paths []string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		paths = append(paths, r.URL.Path+"?"+r.URL.RawQuery)
+
+		if r.URL.Path == "/.well-known/jmap" {
+			// 0.15.5 advertises no urn:stalwart:jmap.
+			json.NewEncoder(w).Encode(map[string]any{
+				"capabilities": map[string]any{"urn:ietf:params:jmap:core": map[string]any{}},
+			})
+			return
+		}
+		if r.URL.Path == "/api" {
+			w.WriteHeader(http.StatusNotFound)
+			w.Write([]byte(`{"status":404,"title":"Not Found"}`))
+			return
+		}
+		if r.URL.Path != "/api/principal" {
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+
+		set := individuals
+		if r.URL.Query().Get("types") == "domain" {
+			set = domains
+		}
+		limit, page := 100, 1
+		fmt.Sscanf(r.URL.Query().Get("limit"), "%d", &limit)
+		fmt.Sscanf(r.URL.Query().Get("page"), "%d", &page)
+
+		start := (page - 1) * limit
+		end := start + limit
+		if start > len(set) {
+			start = len(set)
+		}
+		if end > len(set) {
+			end = len(set)
+		}
+		json.NewEncoder(w).Encode(map[string]any{
+			"data": map[string]any{"items": set[start:end], "total": len(set)},
+		})
+	}))
+	t.Cleanup(srv.Close)
+	return srv, &paths
+}
+
+// The headline case: against the version this tool actually migrates from,
+// AccountSnapshot must not fall over on a 404 from the 0.16-only endpoint.
+func TestAccountSnapshotUsesRESTAgainst015(t *testing.T) {
+	srv, paths := stalwart015Server(t,
+		[]map[string]any{
+			{"id": 4, "type": "individual", "name": "alice", "emails": []string{"[email protected]"}, "usedQuota": 9207},
+			{"id": 5, "type": "individual", "name": "bob", "emails": []string{"[email protected]"}, "usedQuota": 5380},
+		},
+		[]map[string]any{{"id": 1, "type": "domain", "name": "smoke.test"}},
+	)
+	client := &Client{BaseURL: srv.URL, Username: "admin", Password: "hunter2"}
+
+	snap, err := client.AccountSnapshot(context.Background())
+	if err != nil {
+		t.Fatalf("AccountSnapshot against 0.15.x: %v", err)
+	}
+	if snap.AccountCount != 2 {
+		t.Errorf("AccountCount = %d, want 2", snap.AccountCount)
+	}
+	if len(snap.Domains) != 1 || snap.Domains[0] != "smoke.test" {
+		t.Errorf("Domains = %v, want [smoke.test]", snap.Domains)
+	}
+	if snap.UsedQuota["[email protected]"] != 9207 || snap.UsedQuota["[email protected]"] != 5380 {
+		t.Errorf("UsedQuota = %v, want alice 9207 and bob 5380", snap.UsedQuota)
+	}
+	// Message counts genuinely cannot be had from 0.15.x - see principal.go.
+	if len(snap.MailboxCounts) != 0 {
+		t.Errorf("MailboxCounts = %v, want empty: 0.15.x exposes no per-mailbox counts", snap.MailboxCounts)
+	}
+	for _, p := range *paths {
+		if strings.HasPrefix(p, "/api?") {
+			t.Errorf("the 0.16-only JMAP management endpoint was called against a 0.15.x instance: %s", p)
+		}
+	}
+}
+
+// A truncated "before" snapshot would make the post-migration comparison
+// assert less than it claims, silently.
+func TestRESTPrincipalsFollowsPagination(t *testing.T) {
+	var many []map[string]any
+	for i := 0; i < 250; i++ {
+		many = append(many, map[string]any{
+			"id": i, "type": "individual",
+			"name":   fmt.Sprintf("user%03d", i),
+			"emails": []string{fmt.Sprintf("user%[email protected]", i)},
+		})
+	}
+	srv, _ := stalwart015Server(t, many, nil)
+	client := &Client{BaseURL: srv.URL, Username: "admin", Password: "x"}
+
+	snap, err := client.AccountSnapshot(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if snap.AccountCount != 250 {
+		t.Errorf("AccountCount = %d, want all 250 across pages", snap.AccountCount)
+	}
+}
+
+// An instance with no explicit domain principals still has domains, implied
+// by its accounts' addresses.
+func TestRESTSnapshotDerivesDomainsFromAddresses(t *testing.T) {
+	srv, _ := stalwart015Server(t,
+		[]map[string]any{
+			{"id": 1, "type": "individual", "name": "a", "emails": []string{"[email protected]"}},
+			{"id": 2, "type": "individual", "name": "b", "emails": []string{"[email protected]"}},
+		}, nil)
+	client := &Client{BaseURL: srv.URL, Username: "admin", Password: "x"}
+
+	snap, err := client.AccountSnapshot(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(snap.Domains) != 2 || snap.Domains[0] != "one.example" || snap.Domains[1] != "two.example" {
+		t.Errorf("Domains = %v, want [one.example two.example] sorted", snap.Domains)
+	}
+}
+
+func TestRESTSnapshotSurfacesAuthFailure(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/.well-known/jmap" {
+			json.NewEncoder(w).Encode(map[string]any{"capabilities": map[string]any{}})
+			return
+		}
+		w.WriteHeader(http.StatusUnauthorized)
+		w.Write([]byte("invalid credentials"))
+	}))
+	defer srv.Close()
+
+	client := &Client{BaseURL: srv.URL, Username: "admin", Password: "wrong"}
+	_, err := client.AccountSnapshot(context.Background())
+	if err == nil {
+		t.Fatal("want an error when the principal list rejects the credentials")
+	}
+	if !strings.Contains(err.Error(), "401") {
+		t.Errorf("error %q should carry the status it got", err)
+	}
+}
+
+// 0.16 reports the same per-account measure under a different name; both
+// have to land in the same field or the comparison can't span the boundary.
+func TestJMAPSnapshotCapturesUsedDiskQuota(t *testing.T) {
+	srv, _ := accountManagementAndMailboxServer(t, map[string][]map[string]any{
+		"[email protected]": {{"name": "Inbox", "totalEmails": 10}},
+		"[email protected]":   {{"name": "Inbox", "totalEmails": 3}},
+	})
+	defer srv.Close()
+
+	client := &Client{BaseURL: srv.URL, Username: "admin", Password: "hunter2"}
+	snap, err := client.AccountSnapshot(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(snap.UsedQuota) != 2 {
+		t.Errorf("UsedQuota = %v, want an entry per account", snap.UsedQuota)
+	}
+}