Incorrect rendering of windows-1257 encoded emails (Baltic characters broken)

Steps to reproduce

1.Open an email with header:
Content-Type: text/html; charset="windows-1257"
2.View the message in Nextcloud Mail

Expected behavior

Characters should display correctly, for example:

"Dārta Keršule"
"Māris"
"Čau"

Actual behavior

Characters are incorrectly rendered, for example:

"Dârta Kerðule"
"Mâris"
"Èau"

Mail app version

Version 5.7.10, AGPL-licensed

Nextcloud version

Current version is 33.0.0.

Mailserver or service

Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384)

Operating system

Windows 11

PHP engine version

PHP 8.3

Nextcloud memory caching

memcache.local' => '\OC\Memcache\Redis'

Web server

Nginx

Database

MariaDB

Additional info

• The same email displays correctly in other clients (e.g., Thunderbird/Gmail)
• Issue appears only in Nextcloud Mail

email header:

Date: Fri, 20 Mar 2026 10:17:56 +0200
Message-ID:
VE1PR03MB57286337B6AB3ACEBCC5832DC64CA@VE1PR03MB5728.eurprd03.prod.outlook.com
References:
LO0P123MB6416836CF7A5F3156CD3104EAF4EA@LO0P123MB6416.GBRP123.PROD.OUTLOOK.COM
DBBPR03MB10343BE60B980FC14E9C805A1F14FA@DBBPR03MB10343.eurprd03.prod.outlook.com
In-Reply-To:
DBBPR03MB10343BE60B980FC14E9C805A1F14FA@DBBPR03MB10343.eurprd03.prod.outlook.com
Content-Language: en-US
X-MS-Has-Attach: yes
X-MS-Exchange-Organization-SCL: -1
X-MS-TNEF-Correlator:
X-MS-Exchange-Organization-RecordReviewCfmType: 0
msip_labels:
Content-Type: multipart/related;
boundary="002_VE1PR03MB57286337B6AB3ACEBCC5832DC64CAVE1PR03MB5728eurp";
type="text/html"
MIME-Version: 1.0