General ------- Visitor Pattern http://butunclebob.com/ArticleS.UncleBob.IuseVisitor WordPress MU ------------ http://codex.wordpress.org/Create_A_Network http://stackoverflow.com/questions/13960514/how-to-adapt-my-plugin-to-multisite/ Wordpress --------- Internationalizing a Plugin http://codex.wordpress.org/I18n_for_WordPress_Developers Internationalization: You're probably doing it wrong http://ottopress.com/2012/internationalization-youre-probably-doing-it-wrong/ Portable WordPress-only alternative to curl_init http://planetozh.com/blog/2009/08/how-to-make-http-requests-with-wordpress/ "Once the action is complete. I want the page to redirect back to the form that called the script." http://stackoverflow.com/questions/21450966/wp-redirect-call-to-undefined-function-new-plugin "Data Sanitization and Validation With WordPress" http://code.tutsplus.com/articles/data-sanitization-and-validation-with-wordpress--wp-25536 Tutorials --------- "SMTP with oauth for gmail." - Aug 2012 https://skroesbergen.wordpress.com/2012/08/22/smtp-with-oauth-for-gmail/ "GOOGLE, SMTP, AND OAUTH2 AUTHENTICATION" - Feb 2013 http://www.chargenevier.com/2013/02/google-smtp-and-oauth2-authentication/ PHP, SMTP, XOAUTH2 and Gmail - Feb 2014 http://www.boxuk.com/blog/php-smtp-xoauth2-gmail/ SASL XOAUTH2 protocol documentation https://developers.google.com/gmail/xoauth2_protocol Creating a Gmail Token ---------------------- Google Developer OAuth 2.0 Playground https://developers.google.com/oauthplayground/ Google Developers Console https://console.developers.google.com/ Google Apps Security Settings https://admin.google.com/AdminHome?chromeless=1&fral=1#SecuritySettings: Account Permissions https://security.google.com/settings/security/permissions?pli=1 Rereshing a Token ----------------- How do I refresh my google_oauth2 access token using my refresh token? http://stackoverflow.com/questions/12792326/how-do-i-refresh-my-google-oauth2-access-token-using-my-refresh-token References ---------- Using OAuth 2.0 to Access Google APIs https://developers.google.com/accounts/docs/OAuth2 Gmail Platform - OAuth 2.0 https://developers.google.com/gmail/oauth_protocol?hl=nl OAuth Overview -------------- Request Permission -> <- Authorization Grant Grant Code -> <- Authorization Token (Access Token and Refresh Token) wp_mail() and Email in General ----------------------------- The PLAIN Simple Authentication and Security Layer (SASL) Mechanism https://www.ietf.org/rfc/rfc4616.txt What is the difference between ports 465 and 587? http://stackoverflow.com/a/19942206/4368109 The Return Path https://wordpress.org/ideas/topic/wp-mail-and-php-mail-function-according-to-rfc-822 Hacking WordPress Emails http://glennmessersmith.com/pages/wpemail.html The Importance of Content-Type Character Encoding in HTML Emails http://www.emailonacid.com/blog/details/C13/the_importance_of_content-type_character_encoding_in_html_emails The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) http://www.joelonsoftware.com/articles/Unicode.html How to Tell Who Supports SMTP TLS for Email Transmission https://luxsci.com/blog/how-to-tell-who-supports-tls-for-email-transmission.html JavaMail: Keeping IMAPFolder.idle() alive http://stackoverflow.com/questions/4155412/javamail-keeping-imapfolder-idle-alive Reach More People and Improve Your Spam Score: Why Multi-Part Email is Important https://litmus.com/blog/reach-more-people-and-improve-your-spam-score-why-multi-part-email-is-important HTTP Message Headers http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2 Sending a multipart E-Mail using PHP Mailer/wp_mail - not all clients display E-Mail http://stackoverflow.com/questions/22614615/sending-a-multipart-e-mail-using-php-mailer-wp-mail-not-all-clients-display-e The AUTH Command http://www.samlogic.net/articles/smtp-commands-reference-auth.htm SMTP Authentication with Zend http://framework.zend.com/manual/1.12/en/zend.mail.smtp-authentication.html SMTP Authentication [Tutorial] http://www.fehcom.de/qmail/smtpauth.html Zend Mail --------- Getting access to the SMTP session transcript http://zend-framework-community.634137.n4.nabble.com/Zend-Mail-and-SMTP-Status-Code-td644679.html Sending Mail as a background process http://stackoverflow.com/questions/14177500/sending-emails-in-php-and-using-google-apps-mail-as-smtp-is-too-slow PHP Resources ------------- Why your PHP App NEEDS a Circuit Breaker http://devzone.zend.com/1424/why-your-php-app-needs-a-circuit-breaker/ Capturing and Handling PHP Errors Gracefully http://biostall.com/capturing-and-handling-php-errors-gracefully Gmail SMTP Settings and New Security Measures Demystified http://www.wpsitecare.com/gmail-smtp-settings/ Google API ---------- Gmail API https://developers.google.com/gmail/api/ Google APIs Client Library for PHP https://github.com/google/google-api-php-client (Google App Engine) Mail PHP API Overview https://cloud.google.com/appengine/docs/php/mail/ (Google App Engine) Bulk Mail with Analytics via SendGrid https://cloud.google.com/appengine/docs/php/mail/sendgrid