This is a known issue with reCAPTCHA that NLM is not able to resolve.
The workaround is to log into your My NCBI account before sending email. If you are logged in, you won't encounter reCAPTCHA, or this error. Users who are not logged in will continue to encounter the reCAPTCHA and
Information on creating My NCBI account can be found here: https://www.ncbi.nlm.nih.gov/books/NBK3842/#MyNCBI.Registering_with_My_NCBI
