The best replacement for outlook is outlook express.

The best alternatives to outlook are rated as following:
★★★★★  outlook express
★★★★★  thunderbird
★★★★  gmail
★★  postbox
★★  em client
★★  lotus notes
★★  pimero professional
★★  hotmail
★★  entourage
★★  mac mail
★  windows mail
★  windows live mail
★  exchange
★  acadia
★  outlook.com
★  live
★  act
★  google calendar
★  groupwise
★  gmc acadia
  apple mail
  mail
  yahoo
  google
  express
  windows live
  outlook
  google apps
  notes
  windows 8 mail
  outlook exchange
  eudora
  live mail
  google calendar better
  outlook web access
  office 365
  gmail for business
  thunderbird comparison
  gmail better
  google mail
  ical
  onenote
  yahoo mail
  dimensions
  entourage for mac

Your alternative for outlook is not listed? Suggest!
Speaking about outlook, one probably shouldn't forget about business contact manager.

Other search terms related to outlook and their ratings are:
★★★★★ business contact manager
★★★★★ gmail
★★★★ yahoo
★★★★ yahoo mail
★★★★ exchange
★★★★ iphone
★★★ office
★★★ hotmail
★★★ email
★★ google apps
★★ google calendar
★★ icloud
★★ aol
★★ add ins
★★ office 365
★ outlook.com
★ android
★ own domain
★ microsoft account
★ exchange server
★ palm
★ comcast
★ multiple email accounts
subject
godaddy
pst
pst file
an exchange server
skype
microsoft exchange server
active sync
mobileme
bcm
yahoo mail plus
You have in mind a companion for outlook and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of outlook in all years. Click on graph for more.
outlook
outlook express
thunderbird