The following validator is provided by catworkx Extended Group Management:

[cwx] Group Name Validator

Validates that the chosen group name is not empty and is not already used.

Required information:

• Name Field: Select the custom field that stores the group name.
  
  

[cwx] Group Exists Validator

Validates that a group with the chosen name exists.

Required information:

• Name Field: Select the custom field that stores the group name.
   

[cwx] Users Email Validator

Validates that picked users' email address belongs to the required domains.

Required information:

• Name Field: Select the field containing the name of the group.
• Group Name Filter: If the validation should only be performed for selected groups, you can specify a regular expression (following the Java Pattern specification) here to match groups that should be validated.
• Users Field: Select the multi-user picker field to be checked.
• Allowed Domain Name Pattern: Specify a regular expression (using the Java Pattern specification) to match valid domains for the users' email addresses. Users whose email's domain does not match this expression will be rejected by the validator.