devise

Mail::Message#==

Two emails are the same if they have the same fields and body contents. One
gotcha here is that Mail will insert Message-IDs when calling encoded, so doing
mail1.encoded == mail2.encoded is most probably not going to return what you think
as the assigned Message-IDs by Mail (if not already defined as the same) will ensure
that the two objects are unique, and this comparison will ALWAYS return false.

So the == operator has been defined like so:  Two messages are the same if they have
the same content, ignoring the Message-ID field, unless BOTH emails have a defined and
different Message-ID value, then they are false.

So, in practice the == operator works like this:

 m1 = Mail.new("Subject: Hello\r\n\r\nHello")
 m2 = Mail.new("Subject: Hello\r\n\r\nHello")
 m1 == m2 #=> true

 m1 = Mail.new("Subject: Hello\r\n\r\nHello")
 m2 = Mail.new("Message-ID: <1234@test>\r\nSubject: Hello\r\n\r\nHello")
 m1 == m2 #=> true

 m1 = Mail.new("Message-ID: <1234@test>\r\nSubject: Hello\r\n\r\nHello")
 m2 = Mail.new("Subject: Hello\r\n\r\nHello")
 m1 == m2 #=> true

 m1 = Mail.new("Message-ID: <1234@test>\r\nSubject: Hello\r\n\r\nHello")
 m2 = Mail.new("Message-ID: <1234@test>\r\nSubject: Hello\r\n\r\nHello")
 m1 == m2 #=> true

 m1 = Mail.new("Message-ID: <1234@test>\r\nSubject: Hello\r\n\r\nHello")
 m2 = Mail.new("Message-ID: <DIFFERENT@test>\r\nSubject: Hello\r\n\r\nHello")
 m1 == m2 #=> false

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