Issue #2457781 by prateekMehta, stefan.r, AjitS, hussainweb: Use Utility\Html class instead of Utility\String for decodeEntities() function

Issue #1946090 by pjonckiere, alex-mo, rpayanm: _drupal_wrap_mail_line() does not force-wrap too long words after 996 characters

Issue #2225427 by ianthomas_uk, martin107, JeroenT, LoMo: Remove remaining uses of deprecated language functions (mostly in object oriented code)

Issue #2358991 by JeroenT, ianthomas_uk, rpayanm, jamesdixon, er.pushpinderrana, Ashok Negi: Remove usage of drupal_mail()

Issue #2358995 by rpayanm, JeroenT, Alienpruts, gaurav.pahuja, er.pushpinderrana | Les Lim: Remove usage of drupal_wrap_mail().

Issue #2358999 by rpayanm, JeroenT, er.pushpinderrana, javivf, Ec1ipsis, aczietlow | Les Lim: Remove usage of drupal_html_to_text().

Issue #2318281 by tim.plunkett, dawehner | kim.pepper: Provide a standard way to check a plugin is an instance of the required interface.

Issue #2301393 by kim.pepper, larowlan: Deprecate all of mail.inc, move drupal_mail to method on Mail plugin manager.

Issue #950534 by mparker17, mgifford, Mixologic, jbloomfield, erinclerico, theMusician, wmostrey | zirvap: [policy] Consistently use email instead of e-mail in Drupal.

Issue #2053153 by tim.plunkett, dawehner, damiankloip, aspilicious: Allow contrib modules to provide plugins on behalf of optional modules.

Issue #2167109 by Berdir, sun, alexpott, ACF, acrollet, adamdicarlo, Albert Volkman, andreiashu, andyceo, andypost, anenkov, aspilicious, barbun, beejeebus, boombatower, cam8001, chriscalip, chx, cosmicdreams, dagmar, damiankloip, dawehner, deviance, disasm, dixon_, dstol, ebrowet, Gábor Hojtsy, heyrocker, Hydra, ianthomas_uk, japicoder, jcisio, jibran, julien, justafish, jvns, KarenS, kbasarab, kim.pepper, larowlan, Lars Toomre, leschekfm, Letharion, LinL, lirantal, Lukas von Blarer, marcingy, Mike Wacker, mrf, mtift, mtunay, n3or, nadavoid, nick_schuch, Niklas Fiekas, ParisLiakos, pcambra, penyaskito, pfrenssen, plopesc, Pol, Rok Žlender, rvilar, swentel, tim.plunkett, tobiasb, tsvenson, typhonius, vasi1186, vijaycs85, wamilton, webchick, webflo, wizonesolutions, xjm, yched, YesCT, znerol: Remove Variable subsystem.

Issue #1998638 by damiankloip, dawehner, kim.pepper, cosmicdreams, alexpott, larowlan, Damien Tournoud: Replace almost all remaining superglobals (, , etc.) with Symfony Request object.

Issue #1889644 by Berdir: Convert drupal_mail_system() to a MailFactory service to allow more flexible replacements.

Issue #1821420 by vijaycs85, cam8001, Albert Volkman, ACF, typhonius, pcambra, Berdir: Convert mail variables to cmi.

Issue #1326664 by Lars Toomre, Albert Volkman, sven.lauer, tim.plunkett: API docs cleanup for parts of system module and other files

Issue #1471364 by amateescu: Move mail system classes from system.mail.inc to PSR-0 classes in Drupal\Core.