Part One: Written Correspondence
(1) Feel free to sport your doctoral degree in your email signature module, letterhead, or address stamp.
(2) State your doctoral degree in the displayed sender name of your email account, if you really do consider it necessary.
(3) Refrain from including your doctoral degree, or any abbreviation of it, in your email address, such as email@example.com or firstname.lastname@example.org. If at all possible, also avoid writing it on envelopes by hand.
(4) Do not, by all means, sign your correspondence with your doctoral degree attached to your name, regardless of how cordially, sincerely, or respectfully you choose to express your salutation. Your conversation partner will appreciate your modesty. Thanks for your attention.
Part Two: Oral Conversation
(1) Do not introduce yourself with your doctoral degree. (Well, this should go without saying.)
(2) Do not expect others to address you by your doctoral degree.
(3) Do not mention your doctoral degree in non-academic conversations unless requested by a legal authority, Elsa of Brabant, or Master Yoda (»Decently behave you must!«).