[IMAP Backend] Domain missing in SMTPAddress with system user authentication

[whitepig47]

Describe the bug
When using the IMAP backend with system user authentication (e.g., users defined in /etc/passwd), Z-Push fails to include the domain part in the SMTPAddress within the Settings response. This causes iOS devices to treat the account as "send-disabled," resulting in the account appearing without a domain in the iOS settings and the "From" address being missing or non-selectable in the Apple Mail app.

To Reproduce
Steps to reproduce the behavior:

1. Configure Z-Push with BackendIMAP.
2. In backend/imap/config.php, set IMAP_DEFAULTFROM to a domain suffix (e.g., @example.com).
3. Add the Exchange account to an iOS device using a system username (e.g., user1) instead of a full email address.
4. After synchronization, check the account settings on the iPhone.
5. Notice the email address is displayed only as user1 (domain missing).
6. Try to compose a new mail; the account's email address is not available in the "From" field.

Expected behavior
Z-Push should respect the IMAP_DEFAULTFROM setting and return the full email address (username@domain) in the Settings response so that the mobile device can correctly identify the sender's address.

Logs
The WBXML log shows that the server sends an incomplete address:

<Settings:UserInformation>
 <Settings:Get>
  <Settings:EmailAddresses>
   <Settings:SMTPAddress>username</Settings:SMTPAddress>
  </Settings:EmailAddresses>
 </Settings:Get>
</Settings:UserInformation>

It should be:

<Settings:SMTPAddress>username@example.com</Settings:SMTPAddress>

Server (please complete the following information):

• OS: Debian GNU/Linux 11 (bullseye)
• PHP Version: php7.4
• Backend for: IMAP
• and Version: Z-Push 2.6.4+0-0

Smartphone (please complete the following information):

• Device: iPhone
• OS: iOS 26.3.1 (a)
• Mail App: Apple Mail
• Version: N/A

Additional context
The issue lies in src/backend/imap/imap.php. Several methods, including Logon and settingsUserInformation, assign $this->username directly to email address fields without appending the domain.

A suggested fix is to use the existing getDefaultFromValue($username, $domain) function in imap.php to ensure the IMAP_DEFAULTFROM configuration is respected.

imap.php.patch