Validate email address #4
Description
https://documentation.mailgun.com/en/latest/api-email-validation.html#email-validation
Email validation with Mailgun requires a monthly plan (i.e. not pay as you go). It is probably good enough to have a built in validator that checks against a regex.
It might also be helpful to have a 'likely invalid' check that looks for misspellings of common email providers / TLDs. E.g. there are a fair number of @gmaol.com and @example.con that would pass validation, but are clearly typos.
Add a public mail.validate() method that can be called prior to attempting to send an email.