DRY & KISS Principles

What's the main issue with this form validation implementation according to the KISS principle?
function validateForm(formData) {
  const errors = {};
  
  // Email validation
  if (formData.email) {
    const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
    if (!emailRegex.test(formData.email)) {
      errors.email = 'Invalid email format';
    } else {
      const [localPart, domain] = formData.email.split('@');
      if (localPart.length > 64 || domain.length > 255) {
        errors.email = 'Email parts too long';
      } else if (domain.split('.').some(part => part.length > 63)) {
        errors.email = 'Domain parts too long';
      }
    }
  } else {
    errors.email = 'Email is required';
  }
  
  return Object.keys(errors).length === 0;
}
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