diff --git a/apps/api/go.mod b/apps/api/go.mod
index 844d823..d0c6033 100644
--- a/apps/api/go.mod
+++ b/apps/api/go.mod
@@ -20,6 +20,7 @@ require (
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	golang.org/x/net v0.26.0 // indirect
 	golang.org/x/sys v0.23.0 // indirect
+	golang.org/x/text v0.38.0 // indirect
 	modernc.org/gc/v3 v3.0.0-20240107210532-573471604cb6 // indirect
 	modernc.org/libc v1.55.3 // indirect
 	modernc.org/mathutil v1.6.0 // indirect
diff --git a/apps/api/go.sum b/apps/api/go.sum
index 428dc1b..2be94ba 100644
--- a/apps/api/go.sum
+++ b/apps/api/go.sum
@@ -26,13 +26,17 @@ golang.org/x/crypto v0.26.0 h1:RrRspgV4mU+YwB4FYnuBoKsUapNIL5cohGAmSH3azsw=
 golang.org/x/crypto v0.26.0/go.mod h1:GY7jblb9wI+FOo5y8/S2oY4zWP07AkOJ4+jxCqdqn54=
 golang.org/x/mod v0.16.0 h1:QX4fJ0Rr5cPQCF7O9lh9Se4pmwfwskqZfq5moyldzic=
 golang.org/x/mod v0.16.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/mod v0.36.0 h1:JJjpVx6myfUsUdAzZuOSTTmRE0PfZeNWzzvKrP7amb4=
 golang.org/x/net v0.26.0 h1:soB7SVo0PWrY4vPW/+ay0jKDNScG2X9wFeYlXIvJsOQ=
 golang.org/x/net v0.26.0/go.mod h1:5YKkiSynbBIh3p6iOc/vibscux0x38BZDkn8sCUPxHE=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.23.0 h1:YfKFowiIMvtgl1UERQoTPPToxltDeZfbj4H7dVUCwmM=
 golang.org/x/sys v0.23.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/text v0.38.0 h1:sXmwo9DwP3OK9EZ7PqAdaooSGozfl/3a6/xJcbzPRhE=
+golang.org/x/text v0.38.0/go.mod h1:YXZt3QhHUKYT53r2lLKFIVi6Ao1jdzrTR/KQ09qyxF4=
 golang.org/x/tools v0.19.0 h1:tfGCXNR1OsFG+sVdLAitlpjAvD/I6dHDKnYrpEZUHkw=
 golang.org/x/tools v0.19.0/go.mod h1:qoJWxmGSIBmAeriMx19ogtrEPrGtDbPK634QFIcLAhc=
+golang.org/x/tools v0.45.0 h1:18qN3FAooORvApf5XjCXgsuayZOEtXf6JK18I3+ONa8=
 modernc.org/cc/v4 v4.21.4 h1:3Be/Rdo1fpr8GrQ7IVw9OHtplU4gWbb+wNgeoBMmGLQ=
 modernc.org/cc/v4 v4.21.4/go.mod h1:HM7VJTZbUCR3rV8EYBi9wxnJ0ZBRiGE5OeGXNA0IsLQ=
 modernc.org/ccgo/v4 v4.19.2 h1:lwQZgvboKD0jBwdaeVCTouxhxAyN6iawF3STraAal8Y=
diff --git a/apps/api/internal/app/maildir_sync.go b/apps/api/internal/app/maildir_sync.go
index 8127f70..d42edfb 100644
--- a/apps/api/internal/app/maildir_sync.go
+++ b/apps/api/internal/app/maildir_sync.go
@@ -15,8 +15,12 @@ import (
 	"net/textproto"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"time"
+
+	"golang.org/x/text/encoding"
+	"golang.org/x/text/encoding/ianaindex"
 )
 
 type maildirMailbox struct {
@@ -350,8 +354,7 @@ func (a *App) parseMaildirMessage(raw []byte, fallbackTo string) (storedMessage,
 	if err != nil {
 		return storedMessage{}, nil, err
 	}
-	decoder := new(mime.WordDecoder)
-	subject, _ := decoder.DecodeHeader(m.Header.Get("Subject"))
+	subject := decodeMIMEHeader(m.Header.Get("Subject"))
 	if strings.TrimSpace(subject) == "" {
 		subject = "(no subject)"
 	}
@@ -460,23 +463,14 @@ func transferReader(encoding string, r io.Reader) io.Reader {
 }
 
 func partFilename(header textproto.MIMEHeader) string {
-	decoder := new(mime.WordDecoder)
 	if _, params, err := mime.ParseMediaType(header.Get("Content-Disposition")); err == nil {
 		if name := strings.TrimSpace(params["filename"]); name != "" {
-			decoded, _ := decoder.DecodeHeader(name)
-			if decoded != "" {
-				name = decoded
-			}
-			return filepath.Base(name)
+			return filepath.Base(decodeMIMEHeader(name))
 		}
 	}
 	if _, params, err := mime.ParseMediaType(header.Get("Content-Type")); err == nil {
 		if name := strings.TrimSpace(params["name"]); name != "" {
-			decoded, _ := decoder.DecodeHeader(name)
-			if decoded != "" {
-				name = decoded
-			}
-			return filepath.Base(name)
+			return filepath.Base(decodeMIMEHeader(name))
 		}
 	}
 	return ""
@@ -485,16 +479,99 @@ func partFilename(header textproto.MIMEHeader) string {
 func firstAddressParts(value string) (string, string) {
 	items, err := netmail.ParseAddressList(value)
 	if err != nil || len(items) == 0 {
-		return strings.TrimSpace(value), ""
+		// ParseAddressList failed — attempt RFC 2047 decode on the raw header,
+		// then retry parsing. This handles non-standard From headers where
+		// encoded words (e.g. =?UTF-8?B?…?=) cause the initial parse to fail.
+		decoded := decodeMIMEHeader(value)
+		items, err = netmail.ParseAddressList(decoded)
+		if err != nil || len(items) == 0 {
+			// Still unparseable: return the decoded value and try to extract
+			// a display name from the decoded string.
+			email, name := splitNameAndEmail(decoded)
+			return normalizeEmail(email), strings.TrimSpace(name)
+		}
 	}
 	item := items[0]
-	return normalizeEmail(item.Address), strings.TrimSpace(item.Name)
+	// Decode item.Name individually so that non-UTF-8 charsets (e.g. GBK,
+	// Shift_JIS) are handled by our CharsetReader, while the address list
+	// structure is parsed from the raw header (avoiding commas/semicolons
+	// inside decoded display names breaking the parser).
+	return normalizeEmail(item.Address), strings.TrimSpace(decodeMIMEHeader(item.Name))
+}
+
+// decodeMIMEHeader decodes all RFC 2047 encoded words (=?charset?encoding?data?=)
+// in the given header value. Falls back to the original value on any error.
+// Supports non-UTF-8 charsets (e.g. GBK, GB2312, Shift_JIS) via x/text.
+// Per RFC 2047 §6.2, linear whitespace between adjacent encoded words is
+// stripped before decoding.
+func decodeMIMEHeader(value string) string {
+	if !strings.Contains(value, "=?") {
+		return value
+	}
+	// RFC 2047 §6.2: ignore whitespace between adjacent encoded words.
+	collapsed := adjacentEncodedWordSpaceRe.ReplaceAllString(value, "$1$2")
+	decoder := &mime.WordDecoder{
+		CharsetReader: charsetReader,
+	}
+	decoded, err := decoder.DecodeHeader(collapsed)
+	if err != nil {
+		return value
+	}
+	return decoded
+}
+
+// adjacentEncodedWordSpaceRe matches whitespace between two adjacent RFC 2047
+// encoded words. Per RFC 2047 §6.2, this whitespace must be ignored when
+// displaying the header.
+var adjacentEncodedWordSpaceRe = regexp.MustCompile(`(\?=)\s+(=\?)`)
+
+// charsetReader converts a non-UTF-8 charset stream into UTF-8 using x/text encodings.
+func charsetReader(charset string, input io.Reader) (io.Reader, error) {
+	charset = strings.ToLower(strings.TrimSpace(charset))
+	if charset == "utf-8" || charset == "us-ascii" {
+		return input, nil
+	}
+	enc, err := ianaindex.IANA.Encoding(charset)
+	if err != nil {
+		return nil, fmt.Errorf("unsupported charset %q: %w", charset, err)
+	}
+	if enc == nil || enc == encoding.Nop || enc == encoding.Replacement {
+		return nil, fmt.Errorf("unsupported charset %q", charset)
+	}
+	return enc.NewDecoder().Reader(input), nil
+}
+
+// splitNameAndEmail attempts to extract a display name and email address from
+// a string like "Display Name <user@example.com>" or plain "user@example.com".
+func splitNameAndEmail(value string) (string, string) {
+	value = strings.TrimSpace(value)
+	if value == "" {
+		return "", ""
+	}
+	// Try "Name <email>" pattern
+	if idx := strings.LastIndex(value, "<"); idx >= 0 {
+		email := strings.TrimSpace(strings.Trim(value[idx+1:], "> "))
+		name := strings.TrimSpace(strings.Trim(value[:idx], `" `))
+		if strings.Contains(email, "@") {
+			return email, name
+		}
+	}
+	// Plain email or unknown format
+	if strings.Contains(value, "@") {
+		return value, ""
+	}
+	return value, ""
 }
 
 func addressList(value string) []string {
 	items, err := netmail.ParseAddressList(value)
-	if err != nil {
-		return nil
+	if err != nil || len(items) == 0 {
+		// ParseAddressList failed — attempt RFC 2047 decode, then retry.
+		decoded := decodeMIMEHeader(value)
+		items, err = netmail.ParseAddressList(decoded)
+		if err != nil || len(items) == 0 {
+			return nil
+		}
 	}
 	out := make([]string, 0, len(items))
 	for _, item := range items {
diff --git a/apps/web/src/lib/utils.ts b/apps/web/src/lib/utils.ts
index 2bdbcfe..c1002be 100644
--- a/apps/web/src/lib/utils.ts
+++ b/apps/web/src/lib/utils.ts
@@ -25,3 +25,62 @@ export function formatBytes(bytes: number) {
   while (size >= 1024 && idx < units.length - 1) { size /= 1024; idx++ }
   return `${size.toFixed(idx === 0 ? 0 : 1)} ${units[idx]}`
 }
+
+/**
+ * Normalize charset aliases to canonical names supported by the browser's TextDecoder.
+ * Only contains aliases that differ from their canonical name — standard names like
+ * "gb18030", "big5", "euc-kr" are passed through directly to TextDecoder.
+ */
+function normalizeCharset(charset: string): string {
+  const c = charset.toLowerCase().trim()
+  const aliases: Record<string, string> = {
+    "gb2312": "gbk",
+    "x-gbk": "gbk",
+    "euc-cn": "gbk",
+    "hz-gb-2312": "gbk",
+    "shift-jis": "shift_jis",
+    "sjis": "shift_jis",
+    "windows-31j": "shift_jis",
+    "ks_c_5601-1987": "euc-kr",
+    "ksc5601": "euc-kr",
+    "windows-949": "euc-kr",
+    "iso-8859-1": "windows-1252",
+  }
+  const mapped = aliases[c]
+  if (mapped) return mapped
+  // cpXXX / cpXXX windows code pages: cp936→windows-936, cp943→windows-943, etc.
+  if (/^cp\d+$/.test(c)) return "windows-" + c.slice(2)
+  return c
+}
+
+/**
+ * Decode RFC 2047 encoded words in mail headers (e.g. =?UTF-8?B?5byA5ZSu?=).
+ * Handles Base64 (B) and Quoted-Printable (Q) encoding.
+ * Supports non-UTF-8 charsets (e.g. GBK, GB2312, Shift_JIS) via charset alias normalization.
+ * Per RFC 2047 §6.2, linear whitespace between adjacent encoded words is stripped.
+ * Returns the original string unchanged if no encoded words are found or on error.
+ */
+export function decodeMimeHeader(value: string): string {
+  if (!value || !value.includes("=?")) return value
+  // RFC 2047 §6.2: ignore whitespace between adjacent encoded words.
+  const collapsed = value.replace(/(\?=)\s+(=\?)/g, "$1$2")
+  return collapsed.replace(/=\?([^?]+)\?([bBqQ])\?([^?]*)\?=/g, (_match, charset, encoding, encoded) => {
+    try {
+      const lowerEncoding = String(encoding).toLowerCase()
+      let decoded: string
+      if (lowerEncoding === "b") {
+        const sanitized = encoded.replace(/\s+/g, "")
+        const padded = sanitized + "=".repeat((4 - (sanitized.length % 4)) % 4)
+        decoded = atob(padded)
+      } else {
+        decoded = encoded.replace(/_/g, " ").replace(/=([0-9a-fA-F]{2})/g, (_m: string, hex: string) => String.fromCharCode(parseInt(hex, 16)))
+      }
+      const bytes = new Uint8Array(Array.from(decoded, (ch) => ch.charCodeAt(0)))
+      const normalized = normalizeCharset(charset) || "utf-8"
+      const decoder = new TextDecoder(normalized)
+      return decoder.decode(bytes)
+    } catch {
+      return _match
+    }
+  })
+}
diff --git a/apps/web/src/pages/admin.tsx b/apps/web/src/pages/admin.tsx
index 0b5cd9e..cb23b0b 100644
--- a/apps/web/src/pages/admin.tsx
+++ b/apps/web/src/pages/admin.tsx
@@ -4,7 +4,7 @@ import { useSearchParams } from "react-router-dom"
 import { useInfiniteQuery, useMutation, useQuery, useQueryClient } from "@tanstack/react-query"
 import { ArrowRight, CheckCircle2, Circle, Copy, Globe2, Mailbox, MoreHorizontal, Plus, RefreshCcw, Search, ShieldCheck, Trash2, Users } from "lucide-react"
 import { api, AdminUser, Alias, DNSRecord, Domain, Mailbox as MailboxType, MailMessage, MailTemplate, SystemSettings } from "@/lib/api"
-import { cn, formatBytes, formatDate } from "@/lib/utils"
+import { cn, decodeMimeHeader, formatBytes, formatDate } from "@/lib/utils"
 import { Button } from "@/components/ui/button"
 import { Input } from "@/components/ui/input"
 import { Label } from "@/components/ui/label"
@@ -811,9 +811,9 @@ function escapeHtml(value: string) {
 }
 
 function adminSenderDisplayName(message: MailMessage) {
-  const fromName = message.fromName?.trim()
+  const fromName = decodeMimeHeader(message.fromName?.trim() || "")
   if (fromName) return fromName
-  const text = message.from.trim()
+  const text = decodeMimeHeader(message.from.trim())
   const namedAddress = text.match(/^"?([^"<]+?)"?\s*<[^>]+>$/)
   const name = namedAddress?.[1]?.trim()
   if (name) return name
@@ -822,8 +822,9 @@ function adminSenderDisplayName(message: MailMessage) {
 }
 
 function adminSenderTitle(message: MailMessage) {
-  const name = message.fromName?.trim()
-  return name ? `${name} <${message.from}>` : message.from
+  const name = decodeMimeHeader(message.fromName?.trim() || "")
+  const from = decodeMimeHeader(message.from)
+  return name ? `${name} <${from}>` : from
 }
 
 function Stat({ icon, label, value }: { icon: React.ReactNode; label: string; value: React.ReactNode }) {
diff --git a/apps/web/src/pages/mail.tsx b/apps/web/src/pages/mail.tsx
index 399a0e6..c8e7ad6 100644
--- a/apps/web/src/pages/mail.tsx
+++ b/apps/web/src/pages/mail.tsx
@@ -14,7 +14,7 @@ import { useNavigate } from "react-router-dom"
 import type { ImperativePanelHandle } from "react-resizable-panels"
 import { AlignCenter, AlignLeft, AlignRight, Archive, ArrowLeft, Bold, Calendar, Check, ChevronDown, ChevronsUpDown, Clock3, Code2, Copy, Ellipsis, Eraser, Eye, FileText, Forward, Highlighter, Image, Inbox, IndentDecrease, IndentIncrease, Italic, Link, List, ListOrdered, Mail, MailCheck, Moon, PanelLeftClose, PanelLeftOpen, Paperclip, PencilLine, Plus, Quote, Redo2, RefreshCcw, Reply, Search, Send, Settings, Signature, SlidersHorizontal, Smile, Star, Strikethrough, Sun, Tag, Trash2, Type, Underline, Undo2, X } from "lucide-react"
 import { api, Mailbox, MailFolder, MailLabel, MailMessage, SendPayload, DraftPayload, ScheduledSend } from "@/lib/api"
-import { cn, formatBytes, formatDate, formatDateTime } from "@/lib/utils"
+import { cn, decodeMimeHeader, formatBytes, formatDate, formatDateTime } from "@/lib/utils"
 import { applyTheme, getInitialTheme } from "@/lib/theme"
 import { useDisplayMode } from "@/lib/display-mode"
 import { Button } from "@/components/ui/button"
@@ -1306,13 +1306,13 @@ function accountInitial(name: string, email?: string) {
 }
 
 function senderDisplayName(message: MailMessage) {
-  const fromName = message.fromName?.trim()
+  const fromName = decodeMimeHeader(message.fromName?.trim() || "")
   if (fromName) return fromName
   return displayNameFromAddress(message.from)
 }
 
 function displayNameFromAddress(value: string) {
-  const text = value.trim()
+  const text = decodeMimeHeader(value.trim())
   const namedAddress = text.match(/^"?([^"<]+?)"?\s*<[^>]+>$/)
   const name = namedAddress?.[1]?.trim()
   if (name) return name
@@ -1322,8 +1322,9 @@ function displayNameFromAddress(value: string) {
 }
 
 function senderTitle(message: MailMessage) {
-  const name = message.fromName?.trim()
-  return name ? `${name} <${message.from}>` : message.from
+  const name = decodeMimeHeader(message.fromName?.trim() || "")
+  const from = decodeMimeHeader(message.from)
+  return name ? `${name} <${from}>` : from
 }
 
 function MessageRow({