Allow overriding default Net::POP3 read_timeout value

[hspazio]

Problem: Net::POP3 uses a default read_timeout of 60 seconds which can be overridden using read_timeout= method. On an application I work we deal with mailboxes having a large volume of emails and large attachments. Sometimes, depending on the traffic we may get a Net::ReadTimeout error when hitting the 60 seconds limit.

This PR allows specifying the read_timeout configuration for Net::POP3 by passing in the :read_timeout configuration when specifying the retriever.

Mail.defaults do
  retriever_method :pop3, { 
    :address             => "localhost",
    :port                => 995,
    :user_name           => "username",
    :password            => "Secret!",
    :enable_ssl          => true,
    :read_timeout        => 200 }
end

Regarding the spec, I used send to invoke a private method. I saw it being used for some other specs so I figured it could be fine. Is there a better way to test this or it's already good?

Thank you,
Fabio

[hspazio]

Hello @jeremy, is there any updates on this PR?
Thanks! ;)

[jeremy]

Thanks @hspazio 👍