Horde_Mail_Rfc822 validator rejects valid email domains starting with digits (e.g. 180grad-kiel.de) causing "Error when parsing angle address"

[Phillipxh]

Bug description

Nextcloud Mail cannot send any emails when the mail domain starts with a digit (e.g. 180grad-kiel.de). The Horde RFC822 validator rejects these domains as invalid when validate => true is set in Transport.php, even though RFC 1123 explicitly allows domain labels to start with digits.

Steps to reproduce

1. Configure a Nextcloud Mail account with an email address on a domain whose first label starts with a digit (e.g. user@180grad-kiel.de)
2. Attempt to send any email
3. The message stays in the outbox and the following error appears in the log

Error message

Horde_Mime_Exception: Error when parsing angle address.
Horde_Mail_Exception: Error when parsing angle address.
at Horde_Mail_Rfc822->_parseAngleAddr()

Root cause

In vendor/bytestream/horde-mail/lib/Horde/Mail/Transport.php line ~137:

'validate' => $this->eai ? 'eai' : true

The Horde RFC822 parser with validate => true rejects domain labels starting with digits, despite RFC 1123 Section 2.1 explicitly relaxing the RFC 1034 restriction.

Workaround

Change true to false in Transport.php line ~137.

Environment

• Nextcloud: 33.0.3.2
• Mail app: 5.8.1
• PHP: 8.4
• OS: Debian 12

[ChristophWurst]

Thank you for the report

How did you create the ticket? I'm trying to understand how the issue form can be bypassed.

[Phillipxh]

I created it with the GitHub CLI via gh issue create, not through the web UI.
That seems to bypass the issue form and submits a regular issue body instead.
I used that because I already had the report details prepared locally. Sorry for the confusion.