Unable to open mail server configuration for a domain in Plesk UI: The label can only be a string

Symptoms

• Opening the mail server settings for a domain lead to an error:

  PLESK_ERROR: "The label can only be a string."

• The following error show on the stack trace:

  CONFIG_TEXT: a</f/<@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:69:151039
  a</forEach/<@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:12:3762
  a</R/<@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:12:3175
  T@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:12:2206
  T@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:12:2595
  T@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:12:2595
  R@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:12:3142
  forEach@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:12:3745
  f@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:69:150580
  g@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:69:151887
  go@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:60258
  Si@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:119227
  wc@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:108477
  bc@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:108405
  gc@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:108266
  ic@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:105430
  Va@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:46632
  nc@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:102558
  Ko@https://server.example.com/ui-library/plesk-ui-library.min.js?1749014571:35:65575
  k/https://server.example.com/cp/javascript/vendors.js?1749655112:20:5689 k/S<@https://server.example.com/cp/javascript/vendors.js?1749655112:20:4766 k/<@https://server.example.com/cp/javascript/vendors.js?1749655112:20:5681
  ge/ne/<@https://server.example.com/cp/javascript/vendors.js?1749655112:42:19160
  ne@https://server.example.com/cp/javascript/vendors.js?1749655112:42:19147
  oe@https://server.example.com/cp/javascript/vendors.js?1749655112:42:20404
  ae@https://server.example.com/cp/javascript/vendors.js?1749655112:42:25703
     )

• Checking the webmail installation on PSA database, there is a misconfigured webmail:

  # MariaDB [psa]> select * from Webmails;
  MariaDB [psa]> select * from Webmails;
  +----+------------+-----------+---------+---------------+--------------------------+---------+
  | id | product_id | name      | version | release       | docroot                  | enabled | 
  +----+------------+-----------+---------+---------------+--------------------------+---------+
  |  1 | roundcube  | Roundcube | 1.4.15  | not-available | /usr/share/psa-roundcube | true    |
  |  2 |            |           |         |               |                          | false   |
  +----+------------+-----------+---------+---------------+--------------------------+---------+
  2 rows in set (0.01 sec)
   2 rows in set (0.01 sec)

Cause

The misconfigured webmail is causing the wrong variable value, causing the issue loading the mail server settings. 

Resolution

1. Connect to the Plesk server via SSH.

2. Create a backup of your system database:

   # plesk db dump psa > /root/psa_dump.sql

3. Remove the defective entry at webmail configuration, executing the command: 

   # MariaDB [psa]> delete from Webmails where id=2; Query OK, 1 row affected (0.00 sec)

   Note: check the webmail id will match the defective entry at Webmails table, which are with NULL values at product_id, name,version, release and docroot.