Unable to add any DNS record if domain name field contains underscore

Symptoms

• Cannot add any DNS record in Domains > example.com > DNS settings if Domain name field contains underscore in it. Following error appears in Plesk interface:

  PLESK_ERROR: The specified domain name is not valid. You need to specify a valid domain name like domain.com.

• The error like below returned when trying to add record via command line (as an example, NS record is given):

  # plesk bin dns --add example.com -ns '_example.com' -nameserver 'ns1.example.com'
  Incorrect DNS Record parameter values were specified

Cause

This is Plesk bug with ID #PPPM-9013, which is planned to be fixed in product future updates. 

Resolution

Currently workaround for NS-record for Plesk Onyx 17.5 for Linux is available:

1. Connect server via SSH
2. Backup original files:

   # mv /usr/local/psa/admin/plib/Dns/Zone/Rec.php{,.backup}
   # mv /usr/local/psa/admin/plib/Smb/Form/Final/DnsZone/Record.php{,.backup}

3. Download patch-files:

   # wget https://plesk.zendesk.com/hc/article_attachments/360010234173/Rec.php
   # wget https://plesk.zendesk.com/hc/article_attachments/360010183174/Record.php

4. Move patch-files to the corresponding directory:

   # mv Rec.php /usr/local/psa/admin/plib/Dns/Zone/
   # mv Record.php /usr/local/psa/admin/plib/Smb/Form/Final/DnsZone/

5. Set correct permissions:

   # chmod 644 /usr/local/psa/admin/plib/Dns/Zone/Rec.php
   # chmod 644 /usr/local/psa/admin/plib/Smb/Form/Final/DnsZone/Record.php