Email sender authentication

Speaking of authentication in an email delivery, usually we will talk about SPF, DKIM and DMARC. Put aside these fancy acronyms, authentication is basically to prove the sender is the legit sender and the email is not tampered in transit.

SPF (Sender Policy Framework) verifies the email is coming from an authorized server. An SPF record is a DNS TXT record specifying which IPs or servers are allowed to send email from that domain.

DKIM (DomainKeys Identified Mail) proves the email has not been changed in transit and the sender owns the DKIM domain. DKIM is also a TXT record signature that builds trust between the sender and the receiver.

DMARC (Domain-Based Message Authentication Reporting and Conformance) is an added authentication method that uses both SPF and DKIM to verify whether or not an email was actually sent by the owner "from" domain. In order for DMARC to pass, both SPF and DKIM must pass, and at least one of them must be aligned. Gmail and Microsoft adopt DMARC into their filtering methods for None, Quarantine, or Reject policies.

Email etiquette at work

• Always use a greeting and a sign-off 
• Use the person’s name, saying “please” and “thank you” when making requests shows your appreciation.
• Always use an informative subject line
• try starting your subject line with an indication of the type of message you’re writing.
• Don’t write a book in your email
• Organize your message into a bulleted or numbered list and using bold text for key dates or questions that need answers. Do ask all of your questions at once if possible.
• Avoid too many or the wrong recipients
• Don't routinely emailing during off-hours
• Write helpful and useful out-of-office messages
• Don't circulate gossip in email
• Use an professional tone.
• Send emails after proofreading them.

Send Transactional Email

1. Hosted email service
2. Amazon SES
3. SendGrid
4. Mandrill (MailChimp Transactional)
5. Mailgun
6. Mailjet
7. SendinBlue
8. Postmark
9. Campaign Monitor
10. SparkPost
11. Knowtify

https://zapier.com/learn/email-marketing/best-transactional-email-sending-services/

Email address

Email address has two parts, namely local-part and domain part, usually in  local-part "@" domain format.

The local-part of the e-mail address may use any of these ASCII characters:

• Uppercase and lowercase English letters (a-z, A-Z)
• Digits 0 to 9
• Characters ! # $ % & ' * + - / = ? ^ _ ` { | } ~
• Character . (dot, period, full stop) provided that it is not the first or last character, and provided also that it does not appear two or more times consecutively.

The domain part is defined as follows:

The Internet standards (Request for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters a through z (in a case-insensitive manner), the digits 0 through 9, and the hyphen (-). The original specification of hostnames in RFC 952, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. However, a subsequent specification (RFC 1123) permitted hostname labels to start with digits. No other symbols, punctuation characters, or blank spaces are permitted.

The format of email addresses is local-part@domain where the local-part may be up to 64 characters long and the domain name may have a maximum of 253 characters – but the maximum of 256-character length of a forward or reverse path restricts the entire email address to be no more than 254 characters long.

One Javascript Example:
/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/

Backbone validation Example:
email: /^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))$/i,

For more info, check out the following links:
http://en.wikipedia.org/wiki/Email_address
http://stackoverflow.com/questions/2049502/what-characters-are-allowed-in-email-address