wp_mail attachments support only ascii symbols

[Fike]

Hi.
Currently wp_mail() passes it's attachments directly to PHPMailer, and that results in taking file basename as attachment name. Basename seems to behave not normal on non-ascii symbols, for example /сontacts.png (the first 'c' is russian) will be truncated as ontacts.png. Apart from that, even if it would be basename'd correctly, it won't be utf8-encoded as required by standard (=?utf-8?B?base64?=), and that will probably result in broken mails and/or rejected mails.

So i'm proposing to implement functionality for manual attachment naming and/or automatic basenaming filenames and encoding attachment names according to ​standard.

#28407 is tightly bound to this request.

[cbutlerjr]

Would resolving #28407 resolve this?

[ocean90]

#49033 was marked as a duplicate.

[SirLouen]

Reproduction Report

Description

❌ This report can't validate that the issue can be reproduced.

Environment

• WordPress: 6.9-alpha-60093-src
• PHP: 8.2.29
• Server: nginx/1.29.0
• Database: mysqli (Server: 8.4.6 / Client: mysqlnd 8.2.29)
• Browser: Chrome 138.0.0.0
• OS: Windows 10/11
• Theme: Twenty Twenty-Five 1.3
• MU Plugins: None activated
• Plugins:
  • Testing Dolly
  • Test Reports 1.2.0

Testing Instructions

1. Create a PDF name: сontacts.pdf (like in the OP Example)
2. Use the 5th parameter of wp_mail to attach this file
3. ✅ Attachment goes through perfectly.

• Other filenames tests:

✅ 你好.pdf
✅ emoji-📄.pdf
✅ áéíóú.pdf

Actual Results

1. ❌ Error condition not occurring.

Additional Notes

• Given that this is not reproducible anymore, because the PHPMailer library's addAttachment method ​was updated to support more encodings 6 years ago, this is not reproducible anymore. For this reason, I'm closing this as worksforme