diff --git a/.travis.yml b/.travis.yml
index 8600228..4d4a74f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,11 +1,13 @@
 sudo: false
 language: ruby
 rvm:
-- 2.2.1
-- 2.0.0
-- 1.9.3
-before_script:
-- bundle install
+  - 2.4.1
+  - 2.3.4
+  - 2.2.7
+  - 2.0.0
+  - 1.9.3
+before_install:
+  - gem install bundler
 gemfile:
   - gemfiles/mail_2.5.gemfile
   - gemfiles/mail_2.6.gemfile
diff --git a/Gemfile b/Gemfile
index 7fe3730..468b9cf 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,3 +2,8 @@ source 'https://rubygems.org'
 
 # Specify your gem's dependencies in sendgrid-actionmailer.gemspec
 gemspec
+
+if RUBY_VERSION < '2'
+  gem 'public_suffix', '~> 1.4.6'
+  gem 'mime-types', '~> 2.99'
+end
diff --git a/gemfiles/mail_2.5.gemfile.lock b/gemfiles/mail_2.5.gemfile.lock
deleted file mode 100644
index 199d267..0000000
--- a/gemfiles/mail_2.5.gemfile.lock
+++ /dev/null
@@ -1,71 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    sendgrid-actionmailer (0.2.1)
-      mail (~> 2.5)
-      sendgrid-ruby (< 2.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    addressable (2.4.0)
-    appraisal (2.1.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    crack (0.4.3)
-      safe_yaml (~> 1.0.0)
-    diff-lcs (1.2.5)
-    faraday (0.9.2)
-      multipart-post (>= 1.2, < 3)
-    hashdiff (0.3.0)
-    mail (2.5.4)
-      mime-types (~> 1.16)
-      treetop (~> 1.4.8)
-    mime-types (1.25.1)
-    mimemagic (0.3.1)
-    multipart-post (2.0.0)
-    polyglot (0.3.5)
-    rake (11.1.2)
-    rspec (3.2.0)
-      rspec-core (~> 3.2.0)
-      rspec-expectations (~> 3.2.0)
-      rspec-mocks (~> 3.2.0)
-    rspec-core (3.2.3)
-      rspec-support (~> 3.2.0)
-    rspec-expectations (3.2.1)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.2.0)
-    rspec-mocks (3.2.1)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.2.0)
-    rspec-support (3.2.2)
-    safe_yaml (1.0.4)
-    sendgrid-ruby (1.1.6)
-      faraday (~> 0.9)
-      mimemagic
-      smtpapi (~> 0.1)
-    smtpapi (0.1.0)
-    thor (0.19.1)
-    treetop (1.4.15)
-      polyglot
-      polyglot (>= 0.3.1)
-    webmock (1.24.6)
-      addressable (>= 2.3.6)
-      crack (>= 0.3.2)
-      hashdiff
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 2.1.0)
-  bundler (~> 1.6)
-  mail (= 2.5.4)
-  rake
-  rspec (~> 3.2.0)
-  sendgrid-actionmailer!
-  webmock (~> 1.24.6)
-
-BUNDLED WITH
-   1.11.2
diff --git a/gemfiles/mail_2.6.gemfile.lock b/gemfiles/mail_2.6.gemfile.lock
deleted file mode 100644
index 1866f04..0000000
--- a/gemfiles/mail_2.6.gemfile.lock
+++ /dev/null
@@ -1,66 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    sendgrid-actionmailer (0.2.1)
-      mail (~> 2.5)
-      sendgrid-ruby (< 2.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    addressable (2.4.0)
-    appraisal (2.1.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    crack (0.4.3)
-      safe_yaml (~> 1.0.0)
-    diff-lcs (1.2.5)
-    faraday (0.9.2)
-      multipart-post (>= 1.2, < 3)
-    hashdiff (0.3.0)
-    mail (2.6.4)
-      mime-types (>= 1.16, < 4)
-    mime-types (2.99.1)
-    mimemagic (0.3.1)
-    multipart-post (2.0.0)
-    rake (11.1.2)
-    rspec (3.2.0)
-      rspec-core (~> 3.2.0)
-      rspec-expectations (~> 3.2.0)
-      rspec-mocks (~> 3.2.0)
-    rspec-core (3.2.3)
-      rspec-support (~> 3.2.0)
-    rspec-expectations (3.2.1)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.2.0)
-    rspec-mocks (3.2.1)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.2.0)
-    rspec-support (3.2.2)
-    safe_yaml (1.0.4)
-    sendgrid-ruby (1.1.6)
-      faraday (~> 0.9)
-      mimemagic
-      smtpapi (~> 0.1)
-    smtpapi (0.1.0)
-    thor (0.19.1)
-    webmock (1.24.6)
-      addressable (>= 2.3.6)
-      crack (>= 0.3.2)
-      hashdiff
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 2.1.0)
-  bundler (~> 1.6)
-  mail (= 2.6.4)
-  rake
-  rspec (~> 3.2.0)
-  sendgrid-actionmailer!
-  webmock (~> 1.24.6)
-
-BUNDLED WITH
-   1.11.2
diff --git a/sendgrid-actionmailer.gemspec b/sendgrid-actionmailer.gemspec
index a9e353e..d338edf 100644
--- a/sendgrid-actionmailer.gemspec
+++ b/sendgrid-actionmailer.gemspec
@@ -23,7 +23,7 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency 'bundler', '~> 1.6'
   spec.add_development_dependency 'rake'
-  spec.add_development_dependency 'rspec', '~>3.2.0'
+  spec.add_development_dependency 'rspec', '~>3.2'
   spec.add_development_dependency 'appraisal', '~> 2.1.0'
-  spec.add_development_dependency 'webmock', '~> 1.24.6'
+  spec.add_development_dependency 'webmock'
 end