Use mail.Address instead of plain strings

[ivanjaros]

Use mail.Address.String() for headers, where full format works, and use mail.Address.Address for smtp's mail and rcpt methods to make it work with the smtp protocol.

[bosim]

You mean what is done in #132 ?

[ivanjaros]

no. i mean the mail address object should be used in place of string arguments, ie. every occurrence of email should be an object.

[bosim]

Make sense, however it will break existing functionality, and will not make a big difference, since the library anyway use Address.String() for serialization.