RFC2822 specifies that you use parentheses to denote a mailbox list. Use the addr-name spec to specify a display name and the from address.

Check against the raw headers of the mail as @mail.from excludes the display name
Extract shared logic between notifier methods

app/mailers/notification_mailers/also_commented.rb

@@ -5,10 +5,10 @@ module NotificationMailers
     attr_accessor :comment
 
     def set_headers(comment_id)
-      @comment  = Comment.find_by_id(comment_id)
+      @comment = Comment.find_by_id(comment_id)
 
       if mail?
-        @headers[:from] = "#{@comment.author.name} (Diaspora*) <#{AppConfig[:smtp_sender_address]}>"
+        @headers[:from] = "[#{@comment.author.name} (Diaspora*)] <#{AppConfig[:smtp_sender_address]}>"
         @headers[:subject] = truncate(@comment.parent.comment_email_subject, :length => TRUNCATION_LEN)
         @headers[:subject] = "Re: #{@headers[:subject]}"
       end

app/mailers/notification_mailers/base.rb

@@ -2,17 +2,16 @@ module NotificationMailers
   TRUNCATION_LEN = 70
 
   class Base
-    attr_accessor :recipient, :recipient_name, :sender
+    attr_accessor :recipient, :sender
 
     def initialize(recipient_id, sender_id=nil, *args)
       @headers = {}
       @recipient = User.find_by_id(recipient_id)
-      @recipient_name = @recipient.profile.first_name
       @sender = Person.find_by_id(sender_id) if sender_id.present?
 
       log_mail(recipient_id, sender_id, self.class.to_s.underscore)
 
-      with_locale do
+      with_recipient_locale do
         set_headers(*args)
       end
     end
@@ -22,19 +21,19 @@ module NotificationMailers
     end
 
     private
-
     def default_headers
       headers = {
+        :from => AppConfig[:smtp_sender_address],
         :host => "#{AppConfig[:pod_uri]}",
         :to => "\"#{@recipient.name}\" <#{@recipient.email}>"
       }
 
-      headers[:from] = "\"#{@sender.name} (Diaspora)\" <#{AppConfig[:smtp_sender_address]}>" if @sender.present?
+      headers[:from] = "\"#{@sender.name} (Diaspora*)\" <#{AppConfig[:smtp_sender_address]}>" if @sender.present?
 
       headers
     end
 
-    def with_locale(&block)
+    def with_recipient_locale(&block)
       I18n.with_locale(@recipient.language, &block)
     end
 

app/mailers/notification_mailers/comment_on_post.rb

@@ -7,7 +7,7 @@ module NotificationMailers
     def set_headers(comment_id)
       @comment = Comment.find(comment_id)
 
-      @headers[:from] = "#{@comment.author.name} (Diaspora*) <#{AppConfig[:smtp_sender_address]}>"
+      @headers[:from] = "[#{@comment.author.name} (Diaspora*)] <#{AppConfig[:smtp_sender_address]}>"
       @headers[:subject] = truncate(@comment.parent.comment_email_subject, :length => TRUNCATION_LEN)
       @headers[:subject] = "Re: #{@headers[:subject]}"
     end

app/mailers/notification_mailers/confirm_email.rb

@@ -1,7 +1,7 @@
 module NotificationMailers
   class ConfirmEmail < NotificationMailers::Base
     def set_headers
-      @headers[:to] = "#{recipient_name} <#{@recipient.unconfirmed_email}>"
+      @headers[:to] = "#{@recipient.profile.first_name} <#{@recipient.unconfirmed_email}>"
       @headers[:subject] = I18n.t('notifier.confirm_email.subject', :unconfirmed_email => @recipient.unconfirmed_email)
     end
   end

app/mailers/notification_mailers/private_message.rb

@@ -7,7 +7,7 @@ module NotificationMailers
       @conversation = @message.conversation
       @participants = @conversation.participants
 
-      @headers[:from] = "#{@message.author.name} (Diaspora*) <#{AppConfig[:smtp_sender_address]}>"
+      @headers[:from] = "[#{@message.author.name} (Diaspora*)] <#{AppConfig[:smtp_sender_address]}>"
       @headers[:subject] = @conversation.subject.strip
       @headers[:subject] = "Re: #{@headers[:subject]}" if @conversation.messages.size > 1
     end

app/mailers/notifier.rb

@@ -2,11 +2,7 @@ class Notifier < ActionMailer::Base
   helper :application
   helper :markdownify
   helper :notifier
-
-  default :from => AppConfig[:smtp_sender_address]
-
-  include NotifierHelper
-
+  
   def self.admin(string, recipients, opts = {})
     mails = []
     recipients.each do |rec|
@@ -24,71 +20,47 @@ class Notifier < ActionMailer::Base
   end
 
   def started_sharing(recipient_id, sender_id)
-    @notification = NotificationMailers::StartedSharing.new(recipient_id, sender_id)
-
-    with_recipient_locale do
-      mail(@notification.headers)
-    end
+    send_notification(:started_sharing, recipient_id, sender_id)
   end
 
   def liked(recipient_id, sender_id, like_id)
-    @notification = NotificationMailers::Liked.new(recipient_id, sender_id, like_id)
-
-    with_recipient_locale do
-      mail(@notification.headers)
-    end
+    send_notification(:liked, recipient_id, sender_id, like_id)
   end
 
   def reshared(recipient_id, sender_id, reshare_id)
-    @notification = NotificationMailers::Reshared.new(recipient_id, sender_id, reshare_id)
-
-    with_recipient_locale do
-      mail(@notification.headers)
-    end
+    send_notification(:reshared, recipient_id, sender_id, reshare_id)
   end
 
   def mentioned(recipient_id, sender_id, target_id)
-    @notification = NotificationMailers::Mentioned.new(recipient_id, sender_id, target_id)
-
-    with_recipient_locale do
-      mail(@notification.headers)
-    end
+    send_notification(:mentioned, recipient_id, sender_id, target_id)
   end
 
   def comment_on_post(recipient_id, sender_id, comment_id)
-    @notification = NotificationMailers::CommentOnPost.new(recipient_id, sender_id, comment_id)
-
-    with_recipient_locale do
-      mail(@notification.headers)
-    end
+    send_notification(:comment_on_post, recipient_id, sender_id, comment_id)
   end
 
   def also_commented(recipient_id, sender_id, comment_id)
-    @notification = NotificationMailers::AlsoCommented.new(recipient_id, sender_id, comment_id)
-
-    with_recipient_locale do
-      mail(@notification.headers) if @notification.mail?
-    end
+    send_notification(:also_commented, recipient_id, sender_id, comment_id)
   end
 
   def private_message(recipient_id, sender_id, message_id)
-    @notification = NotificationMailers::PrivateMessage.new(recipient_id, sender_id, message_id)
-
-    with_recipient_locale do
-      mail(@notification.headers)
-    end
+    send_notification(:private_message, recipient_id, sender_id, message_id)
   end
 
   def confirm_email(recipient_id)
-    @notification = NotificationMailers::ConfirmEmail.new(recipient_id)
+    send_notification(:confirm_email, recipient_id)
+  end
+
+  private
+  def send_notification(type, *args)
+    @notification = NotificationMailers.const_get(type.to_s.camelize).new(*args)
 
     with_recipient_locale do
       mail(@notification.headers)
     end
   end
 
-  private
   def with_recipient_locale(&block)
     I18n.with_locale(@notification.recipient.language, &block)
   end
-end
+end

app/views/notifier/confirm_email.html.haml

@@ -1,5 +1,5 @@
 %p
-  = t('notifier.hello', :name => @notification.recipient_name)
+  = t('notifier.hello', :name => @notification.recipient.profile.first_name)
 %p
   != t('notifier.confirm_email.click_link', :unconfirmed_email => @notification.recipient.unconfirmed_email)
   %br

app/views/notifier/confirm_email.text.haml

@@ -1,4 +1,4 @@
-!= t('notifier.hello', :name => @notification.recipient_name)
+!= t('notifier.hello', :name => @notification.recipient.profile.first_name)
 
 != t('notifier.confirm_email.click_link', :unconfirmed_email => @notification.recipient.unconfirmed_email)
 != confirm_email_url(:token => @notification.recipient.confirm_email_token)

spec/mailers/notifier_spec.rb

@@ -48,7 +48,7 @@ describe Notifier do
   end
 
   describe ".started_sharing" do
-    let!(:request_mail) {Notifier.started_sharing(bob.id, person.id)}
+    let!(:request_mail) { Notifier.started_sharing(bob.id, person.id) }
 
     it 'goes to the right person' do
       request_mail.to.should == [bob.email]
@@ -172,7 +172,7 @@ describe Notifier do
     end
 
     it "FROM: contains the sender's name" do
-      @mail.from.should == "[#{@cnv.author.name} (Diaspora)] <#{AppConfig[:smtp_sender_address]}>"
+      @mail["From"].to_s.should == "[#{@cnv.author.name} (Diaspora*)] <#{AppConfig[:smtp_sender_address]}>"
     end
 
     it 'SUBJECT: has a snippet of the post contents' do
@@ -207,7 +207,7 @@ describe Notifier do
       end
 
       it "FROM: contains the sender's name" do
-        comment_mail.from.should == "[#{eve.name} (Diaspora)] <#{AppConfig[:smtp_sender_address]}>"
+        comment_mail["From"].to_s.should == "[#{eve.name} (Diaspora*)] <#{AppConfig[:smtp_sender_address]}>"
       end
 
       it 'SUBJECT: has a snippet of the post contents' do
@@ -248,7 +248,7 @@ describe Notifier do
       end
 
       it 'FROM: has the name of person commenting as the sender' do
-        comment_mail.from.should == "[#{eve.name} (Diaspora)] <#{AppConfig[:smtp_sender_address]}>"
+        comment_mail["From"].to_s.should == "[#{eve.name} (Diaspora*)] <#{AppConfig[:smtp_sender_address]}>"
       end
 
       it 'SUBJECT: has a snippet of the post contents' do