diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0b3871dd..137cb59a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@
 ### Bug Fixes
 
 - fix: |用户侧收件箱| 修复 `ENABLE_USER_DELETE_EMAIL` 关闭时用户中心仍显示删除按钮且仍可通过 `/user_api/mails/:id` 删除邮件的问题（#978）
+- fix: |Address| 创建邮箱时统一将配置的前缀转为小写，避免生成包含大写前缀的地址；历史数据需用户自行迁移为小写（#930）
 - fix: |Admin| 修复 `/admin/address` 与 `/admin/users` 在使用完整邮箱（query 长度超过 50 字节）作为搜索条件时报错 `D1_ERROR: LIKE or GLOB pattern too complex` 的问题，长查询自动改用 `instr()` 绕开 D1 的 LIKE pattern 长度限制（#956）
 
 ### Improvements
diff --git a/CHANGELOG_EN.md b/CHANGELOG_EN.md
index 46c4048e..8b10e01a 100644
--- a/CHANGELOG_EN.md
+++ b/CHANGELOG_EN.md
@@ -16,6 +16,7 @@
 ### Bug Fixes
 
 - fix: |User Mailbox| Fix an issue where the user center still showed delete actions and could still delete mail via `/user_api/mails/:id` when `ENABLE_USER_DELETE_EMAIL` was disabled (#978)
+- fix: |Address| Lowercase configured prefixes when creating addresses to avoid generating mixed-case mailbox names; existing data must be migrated to lowercase manually by the user (#930)
 - fix: |Admin| Fix `D1_ERROR: LIKE or GLOB pattern too complex` on `/admin/address` and `/admin/users` when searching by full email address (query length pushes the LIKE pattern over D1's 50-byte limit). Long queries now fall back to `instr()` to bypass the LIKE pattern length cap (#956)
 
 ### Improvements
diff --git a/worker/src/common.ts b/worker/src/common.ts
index 4eb24737..2e503b27 100644
--- a/worker/src/common.ts
+++ b/worker/src/common.ts
@@ -728,13 +728,13 @@ export const commonGetUserRole = async (
 export const getAddressPrefix = async (c: Context<HonoCustomType>): Promise<string | undefined> => {
     const user = c.get("userPayload");
     if (!user) {
-        return getStringValue(c.env.PREFIX);
+        return getStringValue(c.env.PREFIX).trim().toLowerCase();
     }
     const user_role = await commonGetUserRole(c, user.user_id);
     if (typeof user_role?.prefix === "string") {
-        return user_role.prefix;
+        return user_role.prefix.trim().toLowerCase();
     }
-    return getStringValue(c.env.PREFIX);
+    return getStringValue(c.env.PREFIX).trim().toLowerCase();
 }
 
 export const getAllowDomains = async (c: Context<HonoCustomType>): Promise<string[]> => {