Email validation

[bmos]

What is this change?

• Replace validate_email dependency with email-validator.
• Add additional email validation tests.
• _validate_email_string now behaves consistently across python versions.
• Add keyword args to _validate_email_string to allow for optional domain name validation.
• Add keyword args to send_email to allow for optional domain name validation.

Considerations for discussion

• validate_email was last updated in 2015 and has 80 open issues (many with no response from package maintainers).
  It had 2 million downloads in the past month.
• email-validator was last updated in 2025 and has 12 open issues (all of which have been followed-up on).
  It had 174 milliion downloads in the past month.
• It can be helpful to know whether an email server is misconfigured/not real before trying to email it.
  Having domain validation functionality in send_email and _validate_email_string could be helpful.

How to test the changes (if needed)

• CI tests should be adequate

Breaking Changes

Breaking changes are changes to our public API which may require existing users to change their code. If there are no breaking changes, any existing parsons user should not need to do anything after updating their parsons version.

Does this PR introduce breaking changes?

• label: Breaking change — This PR introduces one or more breaking changes.
• label: Non-breaking change — This PR does not introduce one or more breaking changes.

Details (if needed)

• Minor: Emails like "ana@mailserver" (dotless domain names) will now be detected as invalid.
  The old package allowed them, but they are not allowed according to ICANN.

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
parsons/notifications
sendmail.py					304
Project Total

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