Added mail tracking section

SpywareFilter/sections/tracking_servers.txt

@@ -3103,5 +3103,97 @@
 ||yourblocksite.com^
 ||taskapi.net^
 !
+! start: Mail Tracking
+! note that we don't use || prefixes because mail tracking pixels are often proxied by mail providers
+! it's problematic that due to how Gmail proxy work, these domains aren't even exposed on the network level
+! fortunately, extensions can see them (Gmail puts the real URL in the location.hash part of the src)
+! MailTrack
+mailtrack.io/trace/$image
+mltrk.io/pixel$image
+! HubSpot (getsidekick.com)
+t.sidekickopen$image
+t.sigopn$image
+t.senal$image
+t.signaux$image
+t.signauxtrois.com$image
+t.hubspotemail.net/e2t/o$image
+t.hsms06.com$image
+! Boomerang (boomeranggmail.com)
+mailstat.us/tr$image
+! Cirrus Inisght
+tracking.cirrusinsight.com$image
+! Customer.io
+customeriomail.com/e/o$image
+track.customer.io/e/o$image
+! Yesware
+t.yesware.com
+! SalesforceIQ
+salesforceiq.com/t.png$image
+! RelateIQ
+app.relateiq.com/t.png$image
+! Streak
+mailfoogae.appspot.com$image
+! LaunchBit
+launchbit.com/taz-pixel$image
+! MailChimp
+list-manage.com/track$image
+/track/open.php?u=$image
+! Postmark
+cmail1.com/t$image
+pstmrk.it/open$image
+! iContact
+click.icptrack.com/icp/$image
+! Infusionsoft
+infusionsoft.com/app/emailOpened$image
+! Intercom
+via.intercom.io/o$image
+intercom-mail-100.com/o$image
+! Mandrill
+mandrillapp.com/track$image
+! RJ Metrics
+go.rjmetrics.com$image
+! Mixpanel
+api.mixpanel.com/track$image
+! Front App
+web.frontapp.com/api$image
+! ToutApp
+go.toutapp.com$image
+! Outreach
+app.outreach.io$image
+outrch.com/api/mailings/opened$image
+! Mixmax
+track.mixmax.com/api$image
+email.mixmax.com/e/o$image
+! SendGrid
+sendgrid.net/wf/open$image
+/wf/open?upn=$image
+! ExactTarget
+exct.net/open.aspx$image
+! Litmus
+emltrk.com$image
+! dotmailer
+trackedlink.net$image
+! Drip
+dripemail2$image
+! Bananatag
+bl-1.com$image
+! TinyLetter
+tinyletterapp.com$image
+! ContactMonkey
+contactmonkey.com/api/v1/tracker$image
+! Polymail
+welovepg.polymail.io$image
+polymail.io/v2/z$image
+! YAMM
+yamm-track.appspot$image
+! GetResponse
+/open.html?x=$image
+! Close.io
+close.io/email_opened$image
+! Return Path
+returnpath.net/pixel.gif$image
+! NetHunt
+nethunt.com/api/v1/track/email/$image
+!
 !+ NOT_PLATFORM (windows, mac, android)
 ||artfut.com^$empty,important